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A167864 Decimal expansion of Selberg-Delange constant Product_{prime p > 2} (1 + 1/(p(p-2))) 5
1, 5, 1, 4, 7, 8, 0, 1, 2, 8, 1, 3, 7, 4, 9, 1, 2, 5, 7, 7, 9, 0, 9, 1, 9, 2, 5, 5, 6, 4, 9, 4, 7, 4, 8, 9, 2, 4, 1, 5, 2, 7, 0, 1, 5, 8, 2, 8, 6, 2, 1, 4, 3, 9, 5, 3, 5, 7, 4, 8, 4, 2, 7, 1, 4, 8, 4, 9, 3, 2, 2, 0, 9, 8, 1, 5, 6, 1, 1, 5, 8, 1, 0, 8, 7, 7, 5, 8, 5, 3, 8, 2, 7, 6, 9, 8, 0, 7, 6, 7, 7, 6, 5, 6, 2 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Coefficient in formulas for the distribution of integers with a fixed number of prime factors.

Reciprocal of the twin prime constant A005597. See A005597 for links and additional references and comments.

Numerators of partial products are A062271. Denominators are A062270.

An analog for primes of Wallis' product pi/2 = Product_{n >=1} (2n)^2/(2n-1)(2n+1), because A167864 = Product_{prime p>2} (p-1)^2/(p-2)p.

Grosswald (see links) proves that Sum_{k<=x} 2^Omega(k) ~ (1/(8*log(2))) * c * x * (log(x))^2 + O(x * log(x)) where c is this constant. - Amiram Eldar, Jun 06 2020

The asymptotic density of numbers m with A046660(m) = Omega(m) - omega(m) = k is asymptotically ~ c/2^(k+2) as k -> oo, where c is this constant (Rényi, 1955). - Amiram Eldar, Aug 08 2020

REFERENCES

S. R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, 2003, pp. 84-93.

A. Selberg, Note on a paper by L. G. Sathe, J. Indian Math. Soc. 18 (1954) 83-87.

G. Tenenbaum, Introduction to analytic and probabilistic number theory, Cambridge University Press, 1995, p. 206.

LINKS

Table of n, a(n) for n=1..105.

M. Balazard, H. Delange and J.-L. Nicolas, Sur le nombre de facteurs premiers des entiers, C. R. Acad. Sci., Paris, Ser. I 306 (1988) 511-514. [From Jonathan Sondow, Nov 17 2009]

H. Delange, Sur des formules de Atle Selberg, Acta Arith. 19 (1971) 105-146.

S. R. Finch, Mathematical Constants, Errata and Addenda, Sec. 2.1.

Emil Grosswald, The average order of an arithmetic function, Duke Mathematical Journal, Vol. 23, No. 1 (1956), pp. 41-44.

J.-L. Nicolas, Sur la distribution des nombres entiers ayant une quantite fixee de facteurs premiers, Acta Arith. 44 (1984) 191-200.

Alfred Rényi, On the density of certain sequences of integers, Publications de l'Institut Mathématique, Vol. 8 (1955), pp. 157-162.

FORMULA

Equals 1/A005597.

Equals Product_{prime p>2} (p-1)^2/(p-2)p = (2^2/1*3)(4^2/3*5)(6^2/5*7)(10^2/9*11) ....

EXAMPLE

Product_{prime p > 2} (1 + 1/(p(p-2))) = 1.51477...

MATHEMATICA

s[n_] := (1/n)* N[Sum[MoebiusMu[d]*2^(n/d), {d, Divisors[n]}], 160]; C2 = (175/256)*Product[(Zeta[ n]*(1 - 2^(-n))*(1 - 3^(-n))*(1 - 5^(-n))*(1 - 7^(-n)))^(-s[ n]), {n, 2, 160}]; RealDigits[1/C2][[1]][[1 ;; 105]] (* Jean-François Alcover, Oct 30 2012, after Pari program in A005597 *)

$MaxExtraPrecision = 300; digits = 105; terms = 600; P[n_] := PrimeZetaP[n] - 1/2^n; LR = Join[{0, 0}, LinearRecurrence[{3, -2}, {2, 6}, 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 19 2016 *)

PROG

(PARI) prodeulerrat((1 + 1/(p*(p-2))), , 3) \\ Hugo Pfoertner, Aug 08 2020

CROSSREFS

Cf. A005597.

Cf. A001222 (Omega), A046660, A061142 (2^Omega), A069205 (partial sums of 2^Omega).

Sequence in context: A216851 A179290 A342014 * A232809 A011301 A316248

Adjacent sequences:  A167861 A167862 A167863 * A167865 A167866 A167867

KEYWORD

cons,nonn

AUTHOR

Jonathan Sondow, Nov 13 2009, Nov 17 2009

STATUS

approved

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Last modified May 13 00:11 EDT 2021. Contains 343829 sequences. (Running on oeis4.)