A158262 a(n) = coefficient of x^n in the (2^n)-th iteration of x+x^2 for n>=1.

1, 4, 56, 3480, 912640, 969917088, 4106848523904, 68973668731925376, 4597014244761562326272, 1218175506582318206655794688, 1285897546575275148015361075150848

Offset: 1

Author

Paul D. Hanna, Mar 15 2009

Keywords

• nonn

Examples

			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),...;
1,256,65280,16613760,4222658560,1072200161920,272033712041216,(68973668731925376),...;
...
Where the terms in parenthesis form the initial terms of this sequence.
		

Crossrefs

Cf. A158260, A158261, A158263, A158264 (table).

Programs

PARI

{a(n)=local(G=x+x^2+x*O(x^n)); if(n<0, 0, for(i=1, n, G=subst(G, x, G+x*O(x^n))); polcoeff(G, n, x))}