A068219 - OEIS

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A068219

Denominators of coefficients in log(1+x)*(1+x)^(1/3) power series.

3, 3, 9, 3, 15, 9, 21, 6, 27, 15, 33, 9, 39, 21, 45, 12, 51, 27, 57, 15, 63, 33, 69, 18, 75, 39, 81, 21, 87, 45, 93, 24, 99, 51, 105, 27, 111, 57, 117, 30, 123, 63, 129, 33, 135, 69, 141, 36, 147, 75, 153, 39, 159, 81, 165, 42, 171, 87, 177, 45, 183, 93, 189, 48, 195, 99

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OFFSET

1,1

COMMENTS

log(1+x)*(1+x)^(1/3) = (-4)*sum(k=>1,(-x)^k/(3k))

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = 3*n if n==1 or 3 (mod 4), a(n) = 3*n/2 if n==2 (mod 4), a(n) = 3*n/4 if n==0 (mod 4).

a(n) = 3*A060819(n). - Mitch Harris, Jun 29 2005

MATHEMATICA

fn[n_]:=Module[{m=Mod[n, 4]}, Which[OddQ[m], 3n, m==2, 3 n/2, True, 3 n/4]]; Array[fn, 70] (* Harvey P. Dale, Sep 18 2012 *)