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 A301429 Decimal expansion of an analog of the Landau-Ramanujan constant for Loeschian numbers. 17
 6, 3, 8, 9, 0, 9, 4, 0, 5, 4, 4, 5, 3, 4, 3, 8, 8, 2, 2, 5, 4, 9, 4, 2, 6, 7, 4, 9, 2, 8, 2, 4, 5, 0, 9, 3, 7, 5, 4, 9, 7, 5, 5, 0, 8, 0, 2, 9, 1, 2, 3, 3, 4, 5, 4, 2, 1, 6, 9, 2, 3, 6, 5, 7, 0, 8, 0, 7, 6, 3, 1, 0, 0, 2, 7, 6, 4, 9, 6, 5, 8, 2, 4, 6, 8, 9, 7, 1, 7, 9, 1, 1, 2, 5, 2, 8, 6, 6, 4, 3, 8, 8, 1, 4, 1, 6 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS This is the decimal expansion of the number alpha such that the number of positive integers <= N which are represented by the quadratic form x^2 + xy + y^2 is asymptotic to alpha*N/sqrt(log(N)). REFERENCES S. R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, p. 99 (K3). LINKS Peter Luschny, Table of n, a(n) for n = 0..1000 (terms 0..105 from Vaclav Kotesovec). Salma Ettahri, Olivier Ramaré, and Léon Surel, Fast multi-precision computation of some Euler products, arXiv:1908.06808 [math.NT], 2019. Steven R. Finch, Mathematical Constants II, Encyclopedia of Mathematics and Its Applications, Cambridge University Press, Cambridge, 2018, p. 204. Etienne Fouvry, Claude Levesque, and Michel Waldschmidt, Representation of integers by cyclotomic binary forms, arXiv:1712.09019 [math.NT], 2017 and Acta Arithmetica, online 15 March 2018. StackExchange, Iterative calculation of a number-theoretical constant, Mar 24 2018. FORMULA Equals 2^(-1/2)*3^(-1/4)*Product_{p == 2 mod 3, p prime} (1 - p^(-2))^(-1/2). One can base the definition on p(n) = A003627(n). Setting r(n) = (Product_{k=1..n} p(k)^2) / (Product_{k=1..n} (p(k)^2 - 1)) the rational sequence r(n) starts 4/3, 25/18, 605/432, 174845/124416, ... -> L. Then A301429 = sqrt(L)/12^(1/4). - Peter Luschny, Mar 29 2018 [This L is now A333240. - Peter Luschny, Jan 14 2021] Equals Pi*sqrt(2) / (3^(7/4) * sqrt(A175646)). - Vaclav Kotesovec, May 12 2020 Equals 12^(-1/4)*Product_{n>=0} a(-n-2)*b(2^(n+1))^(2^(-n-2)) where a(n) = 3^(2^(n-1))*(1/2-3^(-2^(-n-1))/2)^(2^n) and b(n) = zeta(n)/Im(polylog(n, (-1)^(2/3))). - Peter Luschny, Jan 14 2021 EXAMPLE 0.638909405445343882254942674928245093754975508... MAPLE Digits:= 1000: A:= 2^(-1/2)*3^(-1/4): for t to 40000 do p:= ithprime(t): if `mod`(p, 3) = 2 then A:= evalf(A/(1-1/p^2)^(1/2)) end if end do: A; # Alternative: z := n -> Zeta(n)/Im(polylog(n, (-1)^(2/3))): x := n -> (z(2^n)*(3^(2^n)-1)*sqrt(3)/2)^(1/2^n)/3: evalf(sqrt(mul(x(n), n=1..8))/12^(1/4), 110); # Peter Luschny, Jan 17 2021 MATHEMATICA digits = 106; precision = digits + 10; prodeuler[p_, a_, b_, expr_] := Product[If[a <= p <= b, expr, 1], {p, Prime[Range[PrimePi[a], PrimePi[b]]]}]; Lv3[s_] := prodeuler[p, 1, 2^(precision/s), 1/(1 - KroneckerSymbol[-3, p]*p^-s)] // N[#, precision]&; Lv4[s_] := 2*Im[PolyLog[s, Exp[2*I*Pi/3]]]/Sqrt[3]; Lv[s_] := If[s >= 10000, Lv3[s], Lv4[s]]; gv[s_] := (1 - 3^(-s))*Zeta[s]/Lv[s]; pgv = Product[gv[2^n*2]^(2^-(n + 1)), {n, 0, 11}] // N[#, precision]&; RealDigits[Sqrt[pgv]/12^(1/4), 10, digits][[1]] (* Jean-François Alcover, Jan 12 2021, after PARI code due to Artur Jasinski *) S[m_, n_, s_] := (t = 1; sums = 0; difs = 1; While[Abs[difs] > 10^(-digits - 5) || difs == 0, difs = (MoebiusMu[t]/t) * Log[If[s*t == 1, DirichletL[m, n, s*t], Sum[Zeta[s*t, j/m]*DirichletCharacter[m, n, j]^t, {j, 1, m}]/m^(s*t)]]; sums = sums + difs; t++]; sums); P[m_, n_, s_] := 1/EulerPhi[m] * Sum[Conjugate[DirichletCharacter[m, r, n]] * S[m, r, s], {r, 1, EulerPhi[m]}] + Sum[If[GCD[p, m] > 1 && Mod[p, m] == n, 1/p^s, 0], {p, 1, m}]; Z[m_, n_, s_] := (w = 1; sumz = 0; difz = 1; While[Abs[difz] > 10^(-digits - 5), difz = P[m, n, s*w]/w; sumz = sumz + difz; w++]; Exp[sumz]); \$MaxExtraPrecision = 1000; digits = 121; RealDigits[Chop[N[Pi * Sqrt[2] / (3^(7/4) * Sqrt[Z[3, 1, 2]]), digits]], 10, digits-1][[1]] (* Vaclav Kotesovec, Jan 15 2021 *) z[n_] := Zeta[n]/Im[PolyLog[n, (-1)^(2/3)]]; x[n_] := (z[2^n] (3^(2^n) - 1) Sqrt[3]/2)^(1/2^n)/3; N[Sqrt[Product[x[n], { n, 8}]]/12^(1/4), 110] (* Peter Luschny, Jan 17 2021 *) CROSSREFS Cf. A003136, A003627, A064533, A301430, A333240. Sequence in context: A199447 A273067 A306774 * A198836 A271179 A220085 Adjacent sequences:  A301426 A301427 A301428 * A301430 A301431 A301432 KEYWORD nonn,cons AUTHOR Michel Waldschmidt, Mar 21 2018 EXTENSIONS Offset corrected by Vaclav Kotesovec, Mar 25 2018 a(6)-a(10) from Peter Luschny, Mar 29 2018 More digits from Ettahri article added by Vaclav Kotesovec, May 12 2020 More digits from Vaclav Kotesovec, Jun 27 2020 STATUS approved

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Last modified July 4 11:49 EDT 2022. Contains 355075 sequences. (Running on oeis4.)