A194972 - OEIS

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A194972

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

1, 3, 20, 231, 3864, 85140, 2332616, 76485227, 2921536088, 127421864328, 6248486040840, 340321635330534, 20383240346962440, 1331538898625750100, 94216429100347571448, 7178425650032302557691, 585936966156456139931584, 51011156414845408925712816

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..18.

EXAMPLE

The coefficients of x^k, k>=1, in the odd iterations of x+x^2 begin:

n=1: [(1), 1];

n=3: [1,(3), 6, 9, 10, 8, 4, 1];

n=5: [1, 5,(20), 70, 220, 630, 1656, 4014, 8994, 18654, ...];

n=7: [1, 7, 42,(231), 1190, 5810, 27076, 121023, 520626, ...];

n=9: [1, 9, 72, 540,(3864), 26628, 177744, 1153740, 7303164, ...];