OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..476
FORMULA
E.g.f.: exp(Sum_{j=1..7} x^j).
a(n) = n!*sum(k=1..n, sum(i=0..(n-k)/7, (-1)^i*binomial(k,k-i)*binomial(n-7*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, 7)))
end:
seq(a(n), n=0..23); # Alois P. Heinz, Sep 29 2017
MATHEMATICA
terms = 22;
CoefficientList[E^Total[x^Range[7]] + O[x]^terms, x] Range[0, terms-1]! (* Jean-François Alcover, Nov 11 2020 *)
PROG
(Maxima)
a(n):=if n=0 then 1 else n!*sum(sum((-1)^i*binomial(k, k-i)*binomial(n-7*i-1, k-1), i, 0, (n-k)/7)/k!, k, 1, n);
makelist(a(n), n, 0, 20);
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Aug 09 2011
STATUS
approved