OFFSET
1,2
LINKS
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) = a(n-1)+(n-1)!*(1+n*(n-1)/2) for n>=2.
a(n) = Sum_{k=1..n} k*A100822(n,k).
a(n) = (1/2)*Sum_{j=0..n+1} j! - n!. -Emeric Deutsch,Apr 06 2008
Conjecture D-finite with recurrence a(n) +(-n-4)*a(n-1) +3*(n+1)*a(n-2) +2*(-2*n+3)*a(n-3) +2*(n-3)*a(n-4)=0. -R. J. Mathar,Jul 26 2022
EXAMPLE
a(2)=3 because the deco polyominoes of height 2 are the vertical and horizontal dominoes, having, respectively, 2 and 1 cells in their first columns.
MAPLE
a[1]:=1: for n from 2 to 22 do a[n]:=a[n-1]+(n-1)!*(1+n*(n-1)/2) od: seq(a[n], n=1..22);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch,Aug 09 2006
STATUS
approved