OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..300
FORMULA
From Alois P. Heinz, Jul 23 2014: (Start)
a(n) = n*a(n-1) + n*(n-1)^2*a(n-2) for n>=2, a(0) = a(1) = 1. (End)
Sum_{n>=0} a(n) * x^n / (n!)^2 = exp(x + x^2 / 2). - Ilya Gutkovskiy, Jul 15 2021
MAPLE
a:= proc(n) a(n):= `if`(n<2, 1, n*a(n-1) +n*(n-1)^2*a(n-2)) end:
seq(a(n), n=0..20); # Alois P. Heinz, Jul 23 2014
MATHEMATICA
a[n_] := a[n] = n a[n-1] + n(n-1)^2 a[n-2]; a[0] = a[1] = 1;
a /@ Range[0, 20] (* Jean-François Alcover, Oct 04 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Chad Brewbaker, Mar 27 2014
EXTENSIONS
a(8)-a(9) from Giovanni Resta, Mar 27 2014
a(10)-a(18) from Alois P. Heinz, Jul 23 2014
STATUS
approved