OFFSET
1,3
COMMENTS
a(n)+A121695(n)=n!
REFERENCES
E. Barcucci, S. Brunetti and F. Del Ristoro, Succession rules and deco polyominoes, Theoret. Informatics Appl., 34, 2000, 1-14.
E. Barcucci, A. Del Lungo and R. Pinzani, "Deco" polyominoes, permutations and random generation, Theoretical Computer Science, 159, 1996, 29- 42.
FORMULA
a(n)=a(n-2)+n(n-2)!*floor((n-1)/2) for n>=3; a(1)=0, a(2)=1.
Conjecture D-finite with recurrence a(n) -(n-1)^2*a(n-2) -n*(n-2)*a(n-3)=0. - R. J. Mathar, Jul 22 2022
MAPLE
a[1]:=0: a[2]:=1: for n from 3 to 23 do a[n]:=a[n-2]+n*(n-2)!*floor((n-1)/2) od: seq(a[n], n=1..23);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Aug 17 2006
STATUS
approved