OFFSET
0,4
FORMULA
PROG
(PARI) {a(n)=local(A=matrix(2, 2), B); A[1, 1]=1; for(m=2, n+1, B=matrix(m, m); for(i=1, m, for(j=1, i, if(j==i, B[i, j]=1, if(j==1, B[i, j]=(A^2)[i-1, 1], B[i, j]=(A^2)[i-1, j]-(A^2)[i-1, j-1])); )); A=B); return(A[n+1, 2])}
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Jan 01 2005
STATUS
approved