OFFSET
1,3
COMMENTS
a(n)=Sum(k*A121698(n,k),k=1..n-1).
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
Recurrence relation: a(n)=(2n-3)a(n-1)-(n-1)(n-3)a(n-2)+(n-2)![n-2+(1/2)(1+(-1)^(n-1))(n-1)] for n>=3; a(1)=0, a(2)=1.
Conjecture D-finite with recurrence 16*(n+1)*a(n) +(-16*n^2-178*n+531)*a(n-1) +(-16*n^3+178*n^2-393*n-510)*a(n-2) +(16*n^4+98*n^3-1439*n^2+4222*n-3623)*a(n-3) +(-146*n^4+1479*n^3-4483*n^2+3054*n+2841)*a(n-4) +(130*n-311)*(n-6)*(-4+n)^2*a(n-5)=0. - R. J. Mathar, Jul 26 2022
EXAMPLE
a(2)=1 because the deco polyominoes of height 2 are the vertical and horizontal dominoes, having 1 and 0 columns ending at an even level, respectively.
MAPLE
a[1]:=0: a[2]:=1: for n from 3 to 22 do a[n]:=(2*n-3)*a[n-1]-(n-1)*(n-3)*a[n-2]+(n-2)!*(n-2+(1/2)*(1+(-1)^(n-1))*(n-1)) od: seq(a[n], n=1..22);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Aug 23 2006
STATUS
approved