OFFSET
1,2
COMMENTS
a(n)=Sum(k*A121552(n,k), k=n..1+n(n-1)/2).
REFERENCES
E. Barcucci, A. Del Lungo and R. Pinzani, "Deco" polyominoes, permutations and random generation, Theoretical Computer Science, 159, 1996, 29-42.
FORMULA
a(1)=1; a(n)=n*a(n-1)+(n-1)!*[1+n(n-1)/2] for n>=2 (see Barcucci et al. reference, p. 34).
a(n)=n![n(n-1)/4 + 1/1 + 1/2 + ... +1/n]. - Emeric Deutsch, Apr 06 2008
Conjecture D-finite with recurrence a(n) +(-2*n-3)*a(n-1) +(n^2+4*n-3)*a(n-2) +2*(-n^2+n+3)*a(n-3) +2*(n-3)^2*a(n-4)=0. - R. J. Mathar, Jul 22 2022
MAPLE
a[1]:=1: for n from 2 to 22 do a[n]:=n*a[n-1]+(n-1)!*(1+n*(n-1)/2) od: seq(a[n], n=1..22);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Aug 08 2006
STATUS
approved