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Denominators of partial sums of series for 3*arctanh(1/3) = (3/2)*log(2).
2

%I #10 Sep 01 2013 02:23:11

%S 1,27,405,25515,2066715,7577955,2659862205,71816279535,3662630256285,

%T 626309773824735,2415766270466835,166687872662211615,

%U 7500954269799522675,1822731887561284010025,52859224739277236290725

%N Denominators of partial sums of series for 3*arctanh(1/3) = (3/2)*log(2).

%C Numerators are given in A096949.

%F a(n)=denominator(A(n)) with the rational number A(n):= sum(((1/3)^(2*k))/(2*k+1), k=0..n) in lowest terms.

%e n=10: A096949(10)/2415766270466835 = 2511722368895123/2415766270466835 = 1.039720770838... approximates 3*arctanh(1/3)= 1.039720770840...

%K nonn,easy,frac

%O 0,2

%A _Wolfdieter Lang_, Jul 16 2004