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%I #5 Jun 14 2015 00:42:06
%S 2,6,20,66,222,750,2536,8578,29018,98166,332092,1123458,3800630,
%T 12857438,43496400,147147266,497795634,1684030566,5697034596,
%U 19272929986,65199855118,220569529934,746181374904,2524313509762
%N Logarithmic g.f.: Sum_{n>=1} a(n)/n*x^n = log(G108626(x)), where G108626(x) is g.f. for A108626.
%C A108626 forms the antidiagonal sums of square array A108625, in which row n equals the crystal ball sequence for A_n lattice.
%F G.f.: A(x) = 2*x*(1 - x - x^3)/(1 - 4*x + 2*x^2 + x^4).
%o (PARI) a(n)=polcoeff(2*x*(1-x-x^3)/(1-4*x+2*x^2+x^4+x*O(x^n)),n)
%o (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)
%Y Cf. A108625, A108626.
%K nonn
%O 1,1
%A _Paul D. Hanna_, Jun 13 2005
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