A396485 - OEIS

%I #28 Jul 20 2026 22:36:15

%S 1,2,5,2,6,9,0,6,4,9,1,1,9,7,8,4,4,7,1,3,5,6,6,2,7,7,5,5,5,2,5,1,3,5,

%T 0,9,6,1,7,2,3,8,8,1,8,1,1,8,6,5,7,5,9,4,0,6,5,3,3,7,3,2,2,1,7,4,9,7,

%U 7,2,7,0,5,7,9,0,8,1,5,7,2,2,1,1,6,7,2,0,4,6,6,3,4,4,3,4,0,6,4,4,9,3,3,3,2,1,6,9,3,7,2

%N Decimal expansion of the sum of the reciprocals of doubly triangular numbers (A002817).

%H Kelvin Voskuijl, <a href="/A396485/b396485.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>.

%F Equals 6 - 4*Pi*tanh(sqrt(7)*Pi/2)/sqrt(7).

%e 1.252690649119784...

%t RealDigits[6 - 4*Pi*Tanh[Sqrt[7]*Pi/2]/Sqrt[7], 10, 111][[1]]

%o (PARI) 6 - 4*Pi*tanh(sqrt(7)*Pi/2)/sqrt(7)

%Y Cf. A002817.

%Y Cf. A013661, A002117, A013662.

%K nonn,cons,new

%O 1,2

%A _Kelvin Voskuijl_, Jul 07 2026