A sequence s_n(x) is called a Sheffer sequence iff its generating function has the form sum_(k = 0)^∞ (s_k(x))/(k!) t^k = A(t) e^(x B(t)), where A(t) | = | A_0 + A_1 t + A_2 t^2 + ... B(t) | = | B_1 t + B_2 t^2 + ..., with A_0, B_1 !=0. Sheffer sequences are sometimes also called poweroids (Steffensen 1941, Shiu 1982, Di Bucchianico and Loeb 2000).

Appell cross sequence | Appell sequence | binomial-type sequence | cross sequence | Steffensen sequence | umbral calculus