A108627 Logarithmic g.f.: Sum_{n>=1} a(n)/n*x^n = log(G108626(x)), where G108626(x) is g.f. for A108626.

2, 6, 20, 66, 222, 750, 2536, 8578, 29018, 98166, 332092, 1123458, 3800630, 12857438, 43496400, 147147266, 497795634, 1684030566, 5697034596, 19272929986, 65199855118, 220569529934, 746181374904, 2524313509762

Offset

1,1

Comments

A108626 forms the antidiagonal sums of square array A108625, in which row n equals the crystal ball sequence for A_n lattice.

Links

Table of n, a(n) for n=1..24.

Formula

G.f.: A(x) = 2*x*(1 - x - x^3)/(1 - 4*x + 2*x^2 + x^4).

Prog

(PARI) a(n)=polcoeff(2*x*(1-x-x^3)/(1-4*x+2*x^2+x^4+x*O(x^n)), n)
(PARI) /* Logarithm of g.f. of A108626: */ a(n)=n*polcoeff(log(sum(k=0, n, sum(j=0, k, sum(i=0, j, binomial(k-j, i)^2*binomial(k-i, j-i)))*x^k)+x*O(x^n)), n)

Crossrefs

Cf. A108625, A108626.

Sequence in context: A052991 A246019 A226510 * A193234 A285197 A372872

Adjacent sequences: A108624 A108625 A108626 * A108628 A108629 A108630

Keyword

nonn

Author

Paul D. Hanna, Jun 13 2005

Status

approved