A065470 - OEIS

%I #13 Mar 13 2021 10:04:50

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

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

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

%N Decimal expansion of Product_{p prime} (1 - 1/(p*(p^2-1))).

%H G. Niklasch, <a href="/A001692/a001692.html">Some number theoretical constants: 1000-digit values</a>. [Cached copy]

%e 0.7881625000302207005769495930535...

%t $MaxExtraPrecision = 600; digits = 98; terms = 600; P[n_] := PrimeZetaP[n];

%t LR = Join[{0, 0, 0}, LinearRecurrence[{0, 2, 1, -1, -1}, {-3, 0, -5, -3, -7}, 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 *)

%o (PARI) prodeulerrat(1 - 1/(p*(p^2-1))) \\ _Amiram Eldar_, Mar 13 2021

%Y Cf. A072801.

%K cons,nonn

%O 0,1

%A _N. J. A. Sloane_, Nov 19 2001