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A194971 a(n) equals the coefficient of x^(2*n-1) in the n-th iteration of x+x^2 for n>=1. 1
1, 2, 10, 188, 8994, 832680, 127104492, 28951041456, 9201410927608, 3889680139527920, 2109876998624179100, 1428197506614652750656, 1179911974067256647171268, 1168294604146384807206421176, 1365624160842343461171218423880 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
EXAMPLE
The coefficients of x^k, k>=1, in the n-th iterations of x+x^2 begin:
n=1: [(1), 1];
n=2: [1, 2, (2), 1];
n=3: [1, 3, 6, 9, (10), 8, 4, 1];
n=4: [1, 4, 12, 30, 64, 118, (188), 258, 302, 298, 244,162,84,32,8,1];
n=5: [1, 5, 20, 70, 220, 630, 1656, 4014, (8994), 18654, 35832,...];
n=6: [1, 6, 30, 135, 560, 2170, 7916, 27326, 89582, 279622, (832680), ...]; ...
coefficients in parenthesis form the initial terms of this sequence.
PROG
(PARI) {a(n)=local(A=x, G=x+x^2); for(i=1, n, A=subst(G, x, A+x*O(x^(2*n)))); polcoeff(A, 2*n-1)}
CROSSREFS
Sequence in context: A226563 A037267 A177399 * A155200 A264563 A156510
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 06 2011
STATUS
approved

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Last modified June 22 11:27 EDT 2024. Contains 373570 sequences. (Running on oeis4.)