A334072 Decimal expansion of Sum_{k >= 1} 2^(-sigma(k)), where sigma is the sum of divisors function (A000203).

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

Offset

0,1

Comments

This constant is irrational (Erdős and Graham, 1980).

Links

Table of n, a(n) for n=0..86.

Paul Erdős and Ronald L. Graham, Old and new problems and results in combinatorial number theory, L'enseignement Mathématique, Université de Genève, 1980.

Example

0.71555442225492186679811243819097919331986247102219...

Mathematica

RealDigits[Sum[2^(-DivisorSigma[1, n]), {n, 1, 2000}], 10, 100][[1]]

Prog

(PARI) suminf(k=1, 1/2^sigma(k)) \\ Michel Marcus, Apr 14 2020

Crossrefs

Cf. A000203, A334071.

Sequence in context: A065479 A263202 A011478 * A118307 A351738 A178757

Adjacent sequences: A334069 A334070 A334071 * A334073 A334074 A334075

Keyword

nonn,cons

Author

Amiram Eldar, Apr 13 2020

Status

approved