OFFSET
2,2
EXAMPLE
Table of coefficients in the (2^i)-th iteration of x+x^2 begins:
1,(1);
1,2,(2),1;
1,4,12,(30),64,118,188,258,302,298,244,162,84,32,8,1;
1,8,56,364,(2240),13188,74760,409836,2179556,11271436,56788112,...;
1,16,240,3480,49280,(685160),9383248,126855288,1695695976,...;
1,32,992,30256,912640,27297360,(810903456),23950328688,...;
1,64,4032,252000,15665664,969917088,59855127360,(3683654668512),...;
1,128,16256,2056384,259445760,32668147008,4106848523904,515600292989376,(64657586863790400),...;
...
where the terms in parenthesis form the initial terms of this sequence.
PROG
(PARI) {a(n)=local(G=x+x^2+x*O(x^n)); if(n<2, 0, for(i=1, n-2, G=subst(G, x, G)); polcoeff(G, n, x))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Mar 15 2009
STATUS
approved