A194971 a(n) equals the coefficient of x^(2*n-1) in the n-th iteration of x+x^2 for n>=1.

1, 2, 10, 188, 8994, 832680, 127104492, 28951041456, 9201410927608, 3889680139527920, 2109876998624179100, 1428197506614652750656, 1179911974067256647171268, 1168294604146384807206421176, 1365624160842343461171218423880

Offset

1,2

Links

Table of n, a(n) for n=1..15.

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

Cf. A194972, A122888, A112317.

Sequence in context: A226563 A037267 A177399 * A155200 A264563 A156510

Adjacent sequences: A194968 A194969 A194970 * A194972 A194973 A194974

Keyword

nonn

Author

Paul D. Hanna, Sep 06 2011

Status

approved