OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..485
FORMULA
a(n)=n!*sum(k=1..n, sum(i=0..(n-k)/6, (-1)^i*binomial(k,k-i)*binomial(n-6*i-1,k-1))/k!), n>0, a(0)=1.
MAPLE
a:= proc(n) option remember; `if`(n=0, 1, add(
a(n-j)*binomial(n-1, j-1)*j!, j=1..min(n, 6)))
end:
seq(a(n), n=0..23); # Alois P. Heinz, Sep 29 2017
MATHEMATICA
With[{nn=20}, CoefficientList[Series[Exp[Total[x^Range[6]]], {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Oct 12 2015 *)
PROG
(Maxima)
a(n):=if n=0 then 1 else n!*sum(sum((-1)^i*binomial(k, k-i)*binomial(n-6*i-1, k-1), i, 0, (n-k)/6)/k!, k, 1, n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Aug 09 2011
STATUS
approved