OFFSET
0,2
PROG
(PARI) {a(n)=if(n<0, 0, sum(k=0, n, (matrix(n+1, n+1, m, j, if(m>=j, if(m==j, 1, if(m==j+1, -2*j, polcoeff(1/sum(i=0, m-j, (2*i)!/i!/2^i*x^i)+O(x^m), m-j)))))^-1)[n+1, k+1]))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 16 2005
STATUS
approved