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Denominators of coefficients in log(1+x)*(1+x)^(1/3) power series.
2

%I #12 Sep 21 2018 22:19:12

%S 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,

%T 39,81,21,87,45,93,24,99,51,105,27,111,57,117,30,123,63,129,33,135,69,

%U 141,36,147,75,153,39,159,81,165,42,171,87,177,45,183,93,189,48,195,99

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

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

%H G. C. Greubel, <a href="/A068219/b068219.txt">Table of n, a(n) for n = 1..10000</a>

%F 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).

%F a(n) = 3*A060819(n). - _Mitch Harris_, Jun 29 2005

%t 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 *)

%K easy,frac,nonn

%O 1,1

%A _Benoit Cloitre_, Mar 30 2002