A377960 Expansion of e.g.f. exp(x - x^2)/(1 - x)^3.
1, 4, 17, 82, 469, 3176, 24829, 219262, 2157257, 23405644, 277601161, 3572553194, 49576701277, 737902011952, 11725479449909, 198112664861206, 3546412902136849, 67047080265355412, 1334894917247980417, 27917550541234128514, 611874855066753173861, 14024463626236493578744
Offset: 0
Keywords
Programs
-
PARI
a(n) = n!*sum(k=0, n, binomial(n-2*k+2, n-k)/k!);
Formula
a(n) = n! * Sum_{k=0..n} binomial(n-2*k+2,n-k) / k!.
a(n) = (n+3)*a(n-1) - 3*(n-1)*a(n-2) + 2*(n-1)*(n-2)*a(n-3) for n > 2.