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Sheffer sequences of polynomials and their applications

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Abstract

In this paper, we investigate some properties of several Sheffer sequences of several polynomials arising from umbral calculus. From our investigation, we can derive many interesting identities of several polynomials.

MSC:05A40, 05A19.

1 Introduction

As is well known, the Bernoulli polynomials of order a are defined by the generating function to be

( t e t 1 ) a e x t = n = 0 B n ( a ) (x) t n n ! (see [1–10]),
(1.1)

and the Narumi polynomials are also given by

( log ( 1 + t ) t ) a ( 1 + t ) x = n = 0 N n ( a ) ( x ) n ! t n (see [11, 12]).
(1.2)

In the special case, x=0, N n ( a ) (0)= N n ( a ) are called the Narurni numbers.

Throughout this paper, we assume that λC with λ1. Frobenius-Euler polynomials of order a are defined by the generating function to be

( 1 λ e t λ ) a e x t = n = 0 H n ( a ) (x|λ) t n n ! (see [10–21]).
(1.3)

The Stirling number of the second kind is also defined by the generating function to be

( e t 1 ) n =n! k = n S 2 (k,n) t k k ! (see [9–12]),
(1.4)

and the Stirling number of the first kind is given by

( x ) n =x(x1)(xn+1)= l = 0 n S 1 (n,l) x l (see [9, 11–13]).
(1.5)

Let

F= { f ( t ) = k = 0 a k k ! t k | a k C } .
(1.6)

Let be the algebra of polynomials in the variable x over and P be the vector space of all linear functionals on . The action of the linear functional L on a polynomial p(x) is denoted by L|p(x). We recall that the vector space structures on P are defined by L+M|p(x)=L|p(x)+M|p(x), cL|p(x)=cL|p(x), where c is a complex constant (see [11, 12]).

For f(t)= k = 0 a k t k k ! F, we define a linear functional f(t) on by setting

f ( t ) | x n = a n (n0).
(1.7)

By (1.6) and (1.7), we get

t k | x n =n! δ n , k (n,k0),
(1.8)

where δ n , k is the Kronecker symbol (see [913]).

Suppose that f L (t)= k = 0 L | x k k ! t k . Then we have f L (t)| x n =L| x n and f L (t)=L. Thus, we note that the map L f L (t) is a vector space isomorphism from P onto . Henceforth, will be thought of as both a formal power series and a linear functional. We shall call the umbral algebra. The umbral calculus is the study of umbral algebra (see [913]).

The order o(f(t)) of the non-zero power series f(t) is the smallest integer k for which the coefficient of t k does not vanish. If o(f(t))=1, then f(t) is called a delta series. If o(f(t))=0, then f(t) is called an invertible series. Let o(f(t))=1 and o(g(t))=0. Then there exists a unique sequence S n (x) of polynomials such that g(t)f ( t ) k | S n (x)=n! δ n , k (n,k0). The sequence S n (x) is called Sheffer sequence for (g(t),f(t)), which is denoted by S n (x)(g(t),f(t)). By (1.8), we easily get that e y t |p(x)=p(y). For f(t)F and p(x)P, we have

f(t)= k = 0 f ( t ) | x k k ! t k ,p(x)= k = 0 t k | p ( x ) k ! x k ,
(1.9)

and

f 1 ( t ) f m ( t ) | x n = i 1 + + i m = n ( n i 1 , , i m ) ( j = 1 m f j ( t ) | x i j ) ,
(1.10)

where f 1 (t), f 2 (t),, f m (t)F (see [912]). For f(t),g(t)F and p(x)P, by (1.9), we get

p ( k ) (0)= t k | p ( x ) , 1 | p ( k ) ( x ) = p ( k ) (0).
(1.11)

Thus, by (1.11), we have

t k p(x)= p ( k ) (x)= d k p ( x ) d x k (k0)(see [10–13]).
(1.12)

Let S n (x)(g(t),f(t)). Then we have

1 g ( f ¯ ( t ) ) e y f ¯ ( t ) = k = 0 S k ( y ) k ! t k ,for all yC,
(1.13)

where f ¯ (t) is the compositional inverse of f(t) (see [11, 12]). By (1.2) and (1.13), we see that N n ( a ) (x)( ( e t 1 t ) a , e t 1).

For a0, the Poisson-Charlier sequences are given by

C n (x;a)= k = 0 n ( n k ) ( 1 ) n k a k ( x ) k ( e a ( e t 1 ) , a ( e t 1 ) ) .
(1.14)

In particular, n Z + =N{0}, we have

l = 0 C n (l;a) t l l ! = e t ( t a a ) n (see [11, 12]).
(1.15)

The Frobenius-type Eulerian polynomials of order a are given by

( 1 λ e t ( λ 1 ) λ ) a e x t = n = 0 A n ( a ) (x|λ)(see [11, 19]).
(1.16)

From (1.13) and (1.16), we note that

A n ( a ) (x|λ) ( ( e t ( 1 λ ) λ 1 λ ) a , t ) .

Let us assume that p n (x)(1,f(t)), q n (x)(1,g(t)). Then we have

q n (x)=x ( f ( t ) g ( t ) ) n x 1 p n (x)(see [11, 12]).
(1.17)

Equation (1.17) is important in deriving our results in this paper. The purpose of this paper is to investigate some properties of Sheffer sequences of several polynomials arising from umbral calculus. From our investigation, we can derive many interesting identities of several polynomials.

2 Sheffer sequences of polynomials

Let us assume that S n (x)(g(t),f(t)). Then, by the definition of Sheffer sequence, we see that g(t) S n (x)(1,f(t)). If g(t) is an invertible series, then 1 g ( t ) is also an invertible series. Let us consider the following Sheffer sequences:

M n (x) ( 1 , f ( t ) ) , x n (1,t).
(2.1)

From (1.17) and (2.1), we note that

M n (x)=x ( t f ( t ) ) n x 1 x n =x ( t f ( t ) ) n x n 1 .
(2.2)

For g(t) S n (x)(1,f(t)), by (2.2), we get

g(t) S n (x)=x ( t f ( t ) ) n x n 1 .
(2.3)

Therefore, by (2.3), we obtain the following theorem.

Theorem 2.1 For S n (x)(g(t),f(t)) and n1, we have

S n (x)= 1 g ( t ) x ( t f ( t ) ) n x n 1 .

For example, let S n (x)= D n (x)( 1 λ e t λ , e t 1 e t + 1 ), where D n (x) is the n th Daehee polynomial (see [1, 8, 9]). Then, by Theorem 2.1, we get

D n ( x ) = ( e t λ 1 λ ) x ( t e t 1 ) n ( e t + 1 ) n x n 1 = ( e t λ 1 λ ) x l = 0 n ( n l ) B n 1 ( n ) ( x + l ) = 1 1 λ l = 0 n ( n l ) { ( x + 1 ) B n 1 ( n ) ( x + l + 1 ) λ x B n 1 ( n ) ( x + l ) } .

Let us take S n (x)( ( e t λ 1 λ ) a , t 2 e b t 1 ) (b0). Then, by Theorem 2.1, we get

S n ( x ) = ( 1 λ e t λ ) a x ( e b t 1 t ) n x n 1 = ( 1 λ e t λ ) a x k = 0 n 1 n ! b k + n ( k + n ) ! S 2 ( k + n , n ) x n k 1 ( n 1 ) k = k = 0 n 1 ( n 1 k ) ( k + n n ) S 2 ( k + n , n ) b k + n H n k ( a ) ( x | λ ) .
(2.4)

Therefore, by (2.4), we obtain the following theorem.

Theorem 2.2 For n1, let S n (x)( ( e t λ 1 λ ) a , t 2 e b t 1 ), b0. Then we have

S n (x)= k = 0 n 1 ( n 1 k ) ( k + n n ) S 2 (k+n,n) b k + n H n k ( a ) (x|λ).

Let

S n (x) ( ( e t 1 t ) a , t 2 e b t e c t 1 ) ,c0.
(2.5)

From Theorem 2.1, we can derive

S n ( x ) = ( t e t 1 ) a x ( e c t 1 t e b t ) n x n 1 = ( t e t 1 ) a x e n b t l = 0 n ! S 2 ( l + n , n ) ( l + n ) ! c l + n t l x n 1 = ( t e t 1 ) a x l = 0 n 1 ( n 1 l ) ( l + n l ) S 2 ( l + n , n ) c n + l ( x n b ) n 1 l = ( t e t 1 ) a x l = 0 n 1 j = 0 n 1 l ( n 1 l ) ( l + n l ) ( n 1 l j ) S 2 ( l + n , n ) c n + l ( n b ) j x n 1 l j = l = 0 n 1 j = 0 n 1 l ( n 1 l ) ( l + n l ) ( n 1 l j ) S 2 ( l + n , n ) c n + l ( n b ) j B n l j ( a ) ( x ) .
(2.6)

Therefore, by (2.6), we obtain the following theorem.

Theorem 2.3 For n1, let S n (x)( ( e t 1 t ) a , t 2 e b t e c t 1 ), c0. Then we have

S n (x)= l = 0 n 1 j = 0 n 1 l ( n 1 l ) ( l + n l ) ( n 1 l j ) S 2 (l+n,n) c n + l ( n b ) j B n l j ( a ) (x).

Let us take the following Sheffer sequence:

S n (x) ( ( e t + 1 2 ) α , t 2 log ( 1 + t ) ) .
(2.7)

By Theorem 2.1 and (2.7), we get

S n ( x ) = ( 2 e t + 1 ) α x ( log ( 1 + t ) t ) n x n 1 = ( 2 e t + 1 ) α x l = 0 N l ( n ) l ! t l x n 1 = ( 2 e t + 1 ) α x l = 0 n 1 ( n 1 l ) N l ( n ) x n l 1 = l = 0 n 1 ( n 1 l ) N l ( n ) E n l ( α ) ( x ) ,
(2.8)

where E n ( α ) (x) are the n th Euler polynomials of order α which is defined by the generating function to be

( 2 e t + 1 ) α e x t = n = 0 E n ( α ) (x) t n n ! .

Therefore, by (2.8), we obtain the following theorem.

Theorem 2.4 For n1, let S n (x)( ( e t + 1 2 ) α , t 2 log ( 1 + t ) ). Then we have

S n (x)= l = 0 n 1 ( n 1 l ) N l ( n ) E n l ( α ) (x).

As is known, we note that

( log ( 1 + t ) t ) n =n l = 0 B l ( n + l ) n + l t l l ! .
(2.9)

Thus, by Theorem 2.1 and (2.9), we get

S n ( x ) = ( 2 e t + 1 ) α x ( log ( 1 + t ) t ) n x n 1 = ( 2 e t + 1 ) α x n l = 0 n 1 B l ( n + l ) n + l ( n 1 l ) x n 1 l = n l = 0 n 1 B l ( n + l ) n + l ( n 1 l ) E n l ( α ) ( x ) .
(2.10)

Therefore, by Theorem 2.4 and (2.10), we obtain the following corollary.

Corollary 2.5 For n1, and 0ln1, we have

N l ( n ) n = B l ( n + l ) n + l .

Remark Let S n (x)( ( e t 1 t ) α ,log(1+t)). Then, by Theorem 2.1, we get

S n ( x ) = ( t e t 1 ) α x ( t log ( 1 + t ) ) n x n 1 = ( t e t 1 ) α x l = 0 n 1 ( n 1 l ) N l ( n ) x n 1 l = l = 0 n 1 ( n 1 l ) N l ( n ) B n l ( α ) ( x ) .
(2.11)

Let us assume that

S n (x) ( ( e t λ 1 λ ) α , log ( 1 + t ) ( 1 + t ) c ) (c0).
(2.12)

Then, by Theorem 2.1 and (2.12), we get

S n ( x ) = ( 1 λ e t λ ) α x ( t ( 1 + t ) c log ( 1 + t ) ) n x n 1 = ( 1 λ e t λ ) α x l = 0 n 1 B l ( l n + 1 ) ( c n + 1 ) ( n 1 ) l l ! x n 1 l = l = 0 n 1 ( n 1 l ) B l ( l n + 1 ) ( c n + 1 ) ( 1 λ e t λ ) α x n l = l = 0 n 1 ( n 1 l ) B l ( l n + 1 ) ( c n + 1 ) H n l ( α ) ( x | λ ) .
(2.13)

Therefore, by (2.13), we obtain the following theorem.

Theorem 2.6 For n1, let S n (x)( ( e t λ 1 λ ) α , log ( 1 + t ) ( 1 + t ) c ), c0. Then we have

S n (x)= l = 0 n 1 ( n 1 l ) B l ( l n + 1 ) (cn+1) H n l ( α ) (x|λ).

As is well known, the Bernoulli polynomials of the second kind are defined by the generating function to be

t ( 1 + t ) x log ( 1 + t ) = l = 0 b l ( x ) l ! t l (see [11, 12]).
(2.14)

Thus, by (1.10) and (2.14), we get

( t ( 1 + t ) c log ( 1 + t ) ) n = l = 0 ( l 1 + + l n = l ( l l 1 , , l n ) b l 1 ( c ) b l n ( c ) ) t l l ! .
(2.15)

By Theorem 2.1, (2.12) and (2.15), we get

S n ( x ) = ( 1 λ e t λ ) α x l = 0 n 1 ( l 1 + + l n = l ( l l 1 , , l n ) ( i = 1 n b l i ( c ) ) ( n 1 l ) x n 1 l ) = l = 0 n 1 ( l 1 + + l n = l ( l l 1 , , l n ) ( i = 1 n b l i ( c ) ) ) ( n 1 l ) ( 1 λ e t λ ) α x n l = l = 0 n 1 ( l 1 + + l n = l ( l l 1 , , l n ) ( i = 1 n b l i ( c ) ) ) ( n 1 l ) H n l ( α ) ( x | λ ) .
(2.16)

Therefore, by Theorem 2.6 and (2.16), we obtain the following theorem.

Theorem 2.7 For n1, 0ln1, we have

l 1 + + l n = l ( l l 1 , , l n ) ( i = 1 n b l i ( c ) ) = B l ( l n + 1 ) (cn+1)(c0).

Remark From (1.2), we note that

( t ( 1 + t ) c log ( 1 + t ) ) n x n 1 = l = 0 n 1 ( n 1 l ) N l ( n ) (cn) x n 1 l ,
(2.17)

where c0. By Theorem 2.1, (2.12) and (2.17), we get

S n ( x ) = ( 1 λ e t λ ) α x ( t ( 1 + t ) c log ( 1 + t ) ) n x n 1 = l = 0 n 1 ( n 1 l ) N l ( n ) ( c n ) H n l ( α ) ( x | λ ) .
(2.18)

From (2.16) and (2.18), we can derive the following identity:

N l ( n ) (cn)= l 1 + + l n = l ( l l 1 , , l n ) ( i = 1 n b l i ( c ) ) ,
(2.19)

where n1, 0ln1 and c0. Let

S n (x) ( ( e ( λ 1 ) t λ 1 λ ) α , t 2 ( 1 + t ) c log ( 1 + t ) ) ,c0.
(2.20)

From Theorem 2.1 and (2.20), we note that

S n ( x ) = ( 1 λ e ( λ 1 ) t λ ) α x ( log ( 1 + t ) t ( 1 + t ) c ) n x n 1 = ( 1 λ e ( λ 1 ) t λ ) α x l = 0 n 1 ( n 1 l ) N l ( n ) ( c n ) x n 1 l = l = 0 n 1 ( n 1 l ) N l ( n ) ( c n ) A n l ( α ) ( x | λ ) .
(2.21)

Therefore, by (2.21), we obtain the following proposition.

Proposition 2.8 For n1, let S n (x)( ( e ( λ 1 ) t λ 1 λ ) α , t 2 ( 1 + t ) c log ( 1 + t ) ), c0. Then we have

S n (x)= l = 0 n 1 ( n 1 l ) N l ( n ) (nc) A n l ( α ) (x|λ).

Now we observe that

( log ( 1 + t ) t ( 1 + t ) c ) n = ( 1 + t ) n c ( log ( 1 + t ) t ) n = ( 1 + t ) n c ( k = 0 n ! S 1 ( k + n , n ) ( k + n ) ! t k ) = ( m = 0 ( n c m ) t m ) ( k = 0 n ! S 1 ( k + n , n ) ( k + n ) ! t k ) = l = 0 { k = 0 l n ! S 1 ( k + n , n ) ( k + n ) ! ( n c l k ) } t l .
(2.22)

By Theorem 2.1, (2.20) and (2.22), we get

S n ( x ) = ( 1 λ e ( λ 1 ) t λ ) α x ( log ( 1 + t ) t ( 1 + t ) c ) n x n 1 = l = 0 n 1 ( n 1 l ) l ! { k = 0 l n ! ( k + n ) ! S 1 ( n + k , n ) ( n c l k ) } A n l ( α ) ( x | λ ) .
(2.23)

Therefore, by Proposition 2.8 and (2.23), we obtain the following theorem.

Theorem 2.9 For n1, 0ln1 and c0, we have

N l ( n ) (cn)=l! k = 0 l n ! ( n + k ) ! S 1 (k+n,n) ( n c l k ) .

Remark

It is easy to show that

( log ( 1 + t ) ) n = l = 0 n ! ( l + n ) ! S 1 (l+n,k) t l + n .
(2.24)

By Theorem 2.1, (2.7) and (2.24), we get

S n ( x ) = ( 2 e t + 1 ) α x ( log ( 1 + t ) t ) n x n 1 = ( 2 e t + 1 ) α x l = 0 n 1 n ! l ! ( l + n ) ! ( n 1 l ) S 1 ( l + n , n ) x n 1 l = l = 0 n 1 ( n 1 l ) ( l + n n ) S 2 ( l + n , n ) E n l ( α ) ( x ) .
(2.25)

From Theorem 2.4 and (2.25), we can derive the following identity:

N l ( n ) = S 2 ( l + n , n ) ( l + n n ) ,where n1,0ln1.
(2.26)

Let us consider the following Sheffer sequence:

S n (x) ( ( e ( λ 1 ) t λ 1 λ ) α , t e c t ( 1 + b t ) m ) ,b,c0,m Z + .
(2.27)

By Theorem 2.1 and (2.27), we get

S n ( x ) = ( 1 λ e ( λ 1 ) t λ ) α x ( e c t ( 1 + b t ) m ) n x n 1 = ( 1 λ e ( λ 1 ) t λ ) α x e n c t ( 1 + b t ) m n x n 1 .
(2.28)

From (1.15) and (2.28), we can derive

S n ( x ) = ( 1 λ e ( λ 1 ) t λ ) α x ( 1 ) m n l = 0 n 1 C m n ( l ; n c b ) ( n c ) l ( n 1 l ) x n 1 l = ( 1 ) m n l = 0 n 1 C m n ( l ; n c b ) ( n c ) l ( n 1 l ) A n l ( α ) ( x | λ ) .
(2.29)

Therefore, by (2.29), we obtain the following theorem.

Theorem 2.10 For n1, let S n (x)( ( e ( λ 1 ) t λ 1 λ ) α , t e c t ( 1 + b t ) m ), where m Z + , b0 and c0. Then we have

S n (x)= ( 1 ) m n l = 0 n 1 C m n ( l ; n c b ) ( n c ) l ( n 1 l ) A n l ( α ) (x|λ).

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Acknowledgements

The authors express their sincere gratitude to the referees for their valuable suggestions and comments. This paper is supported in part by the Research Grant of Kwangwoon University in 2013.

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Correspondence to Taekyun Kim.

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Keywords

  • Bernoulli polynomial
  • Euler polynomial
  • Frobenius-Euler polynomial
  • Frobenius-type Eulerian polynomial
  • Sheffer sequence