OFFSET
0,3
EXAMPLE
[1,1,1],[1,1,2],[1,2,2],[1,2,3] are the a(3)=4 sequences.
PROG
(PARI) a(n)=local(p0, p1, p2); if(n<0, 0, p1=1; polcoeff(sum(i=0, n, if(p2=(1-x)*p1-x^2*p0, p0=p1; p1=p2; x^i/p0), x*O(x^n)), n))
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Oct 01 2003
STATUS
approved