OFFSET
0,2
PROG
(PARI) {a(n)=local(A=[1], B); for(i=1, n, A=concat(A, 0); B=Vec(Ser(A)^(2^(#A-2))); A[ #A]=(B[ #B-1]-B[ #B])/2^(#A-2)); Vec(Ser(A)^2)[n+1]}
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Oct 25 2007
STATUS
approved