OFFSET
1,2
COMMENTS
A deco polyomino is a directed column-convex polyomino in which the height, measured along the diagonal, is attained only in the last column.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..440
E. Barcucci, A. Del Lungo and R. Pinzani, "Deco" polyominoes, permutations and random generation, Theoretical Computer Science, 159, 1996, 29-42.
FORMULA
a(n) = 2^(n-1) * (1 + Sum_{j=1..n-1} j*j!/2^j ).
a(n) = (n-1)!*(n-1) + 2*a(n-1) with a(1) = 1.
a(n) = Sum_{k=1..n} k*A140709(n,k).
(1 + x + 2*x^2 + 4*x^3 + 8*x^4 + ...)*(1 + 2*x + 6*x^2 + 24*x^3 + 120*x^4 + ...) = (1 + 3*x + 10*x^2 + 38*x^3 + 172*x^4 + ...) which is (Sum_{n>=0} A011782(n)*x^n) * (Sum_{n>=0} A000142(n+1)*x^n) = Sum_{n>=0} a(n+1)*x^n. - Gary W. Adamson, Feb 24 2012
a(n) = Sum_{j=0..n} (j+1)!*A011782(n-j) = (n+1)! + Sum_{j=0..n-1} 2^(n-k-1)*(j+1)!. - G. C. Greubel, May 03 2021
D-finite with recurrence a(n) +(-n-3)*a(n-1) +3*n*a(n-2) +2*(-n+2)*a(n-3)=0. - R. J. Mathar, Jul 26 2022
EXAMPLE
a(3)=10 because the 6 deco polyominoes of height 3 have columns ending at levels 3, 22, 12, 111, 22, 122, respectively and 1+2+1+3+2+1=10.
MAPLE
a:=proc(n) options operator, arrow: 2^(n-1)*(1+sum(j^2*factorial(j-1)/2^j, j= 1..n-1)) end proc: seq(a(n), n=1..20);
MATHEMATICA
Table[2^(n-1)*(1 + Sum[j*j!/2^j, {j, n-1}]), {n, 30}] (* G. C. Greubel, May 02 2021 *)
PROG
(Magma) [2^(n-1)*(&+[j*Factorial(j)/2^j: j in [1..n-1]]): n in [1..30]]; // G. C. Greubel, May 02 2021
(Sage) [2^(n-1)*sum(j*factorial(j)/2^j for j in (1..n-1)) for n in (1..30)] # G. C. Greubel, May 02 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jun 03 2008
STATUS
approved