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 A158262 a(n) = coefficient of x^n in the (2^n)-th iteration of x+x^2 for n>=1. 4
 1, 4, 56, 3480, 912640, 969917088, 4106848523904, 68973668731925376, 4597014244761562326272, 1218175506582318206655794688, 1285897546575275148015361075150848 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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),...; 1,256,65280,16613760,4222658560,1072200161920,272033712041216,(68973668731925376),...; ... 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<0, 0, for(i=1, n, G=subst(G, x, G+x*O(x^n))); polcoeff(G, n, x))} CROSSREFS Cf. A158260, A158261, A158263, A158264 (table). Sequence in context: A007726 A113113 A186252 * A300513 A089035 A327145 Adjacent sequences:  A158259 A158260 A158261 * A158263 A158264 A158265 KEYWORD nonn AUTHOR Paul D. Hanna, Mar 15 2009 STATUS approved

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Last modified May 31 00:53 EDT 2020. Contains 334747 sequences. (Running on oeis4.)