OFFSET
0,2
PROG
(PARI) a(n)=local(A, B); A=Mat(1); for(m=2, n+4, B=matrix(m, m); for(i=1, m, for(j=1, i, if(i<3 || j==1 || j==i, B[i, j]=1, B[i, j]=A[i-1, j-1]+(A^2)[i-2, j-1] ); )); A=B); (A^2)[n+4, 4]
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 12 2005
STATUS
approved