OFFSET
0,3
COMMENTS
Let A(x) = Sum_{n>=0} a(n) * x^n / n!^2. Then A(x)^2 = A'(x) + x * A''(x). - Michael Somos, May 20 2018
PROG
(PARI) a(n)=if(n==0, 1, sum(k=0, n-1, a(k)*a(n-k-1)*binomial(n-1, k)^2 ))
(PARI) {a(n) = my(A); if( n<0, 0, A = 1 + O(x); for( k=0, n, A = 1 + intformal( intformal(A^2) / x)); n!^2 * polcoeff(A, n))}; /* Michael Somos, May 20 2018 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 15 2007
STATUS
approved