OFFSET
1,2
LINKS
G. Niklasch, Some number theoretical constants: 1000-digit values. [Cached copy]
FORMULA
Equals Sum_{k>=1} mu(k)^2/sigma(k)^2, where mu is the Möbius function (A008683) and sigma(k) is the sum of divisors of k (A000203). - Amiram Eldar, Jan 14 2022
EXAMPLE
1.26655850147152857161454711262964...
MATHEMATICA
$MaxExtraPrecision = 800; digits = 99; terms = 800; P[n_] := PrimeZetaP[n]; LR = LinearRecurrence[{-3, -4, -2}, {0, 0, 2}, terms + 10]; r[n_Integer] := LR[[n]]; Exp[NSum[r[n]*P[n - 1]/(n - 1), {n, 3, terms}, NSumTerms -> terms, WorkingPrecision -> digits + 10]] // RealDigits[#, 10, digits]& // First (* Jean-François Alcover, Apr 18 2016 *)
PROG
(PARI) prodeulerrat(1 + 1/(p+1)^2) \\ Amiram Eldar, Mar 15 2021
CROSSREFS
KEYWORD
cons,nonn
AUTHOR
N. J. A. Sloane, Nov 19 2001
STATUS
approved