OFFSET
3,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 3..500
FORMULA
E.g.f.: exp(Sum_{j=1..3} x^j/j!) - exp(Sum_{j=1..2} x^j/j!).
MAPLE
G:= proc(n, k) option remember; local j; if k>n then G(n, n)
elif n=0 then 1 elif k<1 then 0 else G(n-k, k);
for j from k-1 to 1 by -1 do %*(n-j)/j +G(n-j, k) od; % fi
end:
a:= n-> G(n, 3)-G(n, 2):
seq(a(n), n=3..30);
MATHEMATICA
b[n_, i_] := b[n, i] = If[n==0, 1, If[i<1, 0, Sum[b[n - i j, i - 1] n!/ i!^j/(n - i j)!/j!, {j, 0, n/i}]]];
a[n_] := b[n, 3] - b[n, 2];
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 17 2013
STATUS
approved