OFFSET
0,2
FORMULA
a(n) = Sum_{k=1..n} n!(k!+1) / k!(n-k)! = Sum_{k=1..n} P(n, k)+2^n-1 = A007526(n) - A000225(n) - 1 = A097656(n) - 2.
Conjecture: a(n) +(-n-6)*a(n-1) +(6*n+7)*a(n-2) +(-13*n+14)*a(n-3) +4*(3*n-8)*a(n-4) +4*(-n+4)*a(n-5)=0. - R. J. Mathar, May 29 2013
EXAMPLE
a(2) = 7 because P(2,1) = 2, P(2,2) = 2 while C(2,1)= 2, C(2,2) = 1 and 2 + 2 + 2 + 1 = 7.
MAPLE
MATHEMATICA
f[n_] := Sum[n!(k! + 1)/(k!(n - k)!), {k, n}]; Table[ f[n], {n, 0, 20}] (* Robert G. Wilson v, Sep 24 2004 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Ross La Haye, Sep 21 2004
EXTENSIONS
Edited by Robert G. Wilson v, Sep 24 2004
STATUS
approved