A065486 Decimal expansion of Product_{p prime} (1 + 1/(p+1)^2).

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

Offset: 1

Author

N. J. A. Sloane, Nov 19 2001

Keywords

• cons
• nonn

Examples

			1.26655850147152857161454711262964...
		

Links

• G. Niklasch, Some number theoretical constants: 1000-digit values. [Cached copy]

Crossrefs

Cf. A000203, A008683, A067009.

Programs

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 *)

PARI

prodeulerrat(1 + 1/(p+1)^2) \\ Amiram Eldar, Mar 15 2021

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