A096950 Denominators of partial sums of series for 3*arctanh(1/3) = (3/2)*log(2).

1, 27, 405, 25515, 2066715, 7577955, 2659862205, 71816279535, 3662630256285, 626309773824735, 2415766270466835, 166687872662211615, 7500954269799522675, 1822731887561284010025, 52859224739277236290725

Offset: 0

Author

Wolfdieter Lang, Jul 16 2004

Keywords

• nonn
• easy
• frac

Comments

Numerators are given in A096949.

Examples

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

Formula

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.