A396485 Decimal expansion of the sum of the reciprocals of doubly triangular numbers (A002817).

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, 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, 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

Offset

1,2

Links

Kelvin Voskuijl, Table of n, a(n) for n = 1..10000

Index entries for transcendental numbers.

Formula

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

Example

1.252690649119784...

Mathematica

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

Prog

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

Crossrefs

Cf. A002817.

Cf. A013661, A002117, A013662.

Sequence in context: A242403 A179015 A195621 * A267090 A067948 A142148

Adjacent sequences: A396482 A396483 A396484 * A396486 A396487 A396488

Keyword

nonn,cons,new

Author

Kelvin Voskuijl, Jul 07 2026

Status

approved