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A334072
Decimal expansion of Sum_{k >= 1} 2^(-sigma(k)), where sigma is the sum of divisors function (A000203).
1
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
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
Sequence in context: A065479 A263202 A011478 * A118307 A351738 A178757
KEYWORD
nonn,cons
AUTHOR
Amiram Eldar, Apr 13 2020
STATUS
approved