A polynomial A_n(x;a) given by the associated Sheffer sequence with f(t) = t e^(a t), given by A_n(x;a) = x(x - a n)^(n - 1). The generating function is sum_(k = 0)^∞ (A_k(x;a))/(k!) t^k = e^(x W(a t)/a), where W(x) is the Lambert W-function.