%I A108555
%S A108555 1,2,5,12,35,116,411,1482,5333,19030,67265,235704,819863,2834600,
%T A108555 9752951,33428054,114228713,389419114,1325155261,4503031332,15285291851,
%U A108555 51842203804,175719341971,595316455842,2016131645245,6826076021310
%N A108555 Antidiagonal sums of square array A108553, in which row n equals the 
               crystal ball sequence for D_n lattice.
%C A108555 Limit a(n+1)/a(n) ~ 3.3829757679..., real root of cubic (1+x+3*x^2-x^3).
%o A108555 (PARI) {a(n)=if(n<0,0,if(n==0,1,sum(k=0,n,sum(j=0,k,binomial(n-j,k-j)* 
               (binomial(2*(n-k),2*j)-2*j*(n-k-j)*binomial(n-k,j)/if(n==k+1,1,(n-k-1)))))))}
%Y A108555 Cf. A108553, A108554.
%Y A108555 Sequence in context: A000104 A000105 A055192 this_sequence A032203 A094717 
               A038142
%Y A108555 Adjacent sequences: A108552 A108553 A108554 this_sequence A108556 A108557 
               A108558
%K A108555 nonn
%O A108555 0,2
%A A108555 Paul D. Hanna (pauldhanna(AT)juno.com), Jun 10 2005