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 A307209 Decimal expansion of Product_{i>=1, j>=1} (1 + 1/(i^3 + j^3)). 3
 3, 5, 0, 4, 7, 8, 2, 9, 9, 9, 3, 3, 9, 7, 2, 8, 3, 7, 5, 8, 9, 1, 1, 2, 0, 5, 7, 0, 4, 3, 8, 0, 6, 1, 2, 5, 5, 8, 3, 8, 9, 3, 2, 4, 7, 8, 6, 2, 7, 1, 2, 7, 5, 3, 5, 4, 1, 9, 9, 4, 6, 2, 6, 6, 1, 4, 0, 5, 8, 3, 8, 5, 0, 3, 5, 0, 3, 4, 7, 5, 6, 3, 5, 2, 7, 4, 7, 5, 0, 9, 5, 0, 5, 1, 3, 7, 8, 9, 1, 7, 8, 4, 5, 9, 7 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Product_{i>=1, j>=1} (1 + 1/(i^2 + j^2)) is divergent. A324443(n) / A324403(n) ~ c * n^(Pi/2), where c = A306398 * 2^(3/4) * exp(-Pi/12) * Pi^(1/4) * Gamma(3/4) = 0.36753062884677326134620846786416595535234038999313... Product_{i=1..n, j=1..n} (1 + 1/(i + j)) = A324444(n) / A079478(n) ~ 2^(2*n + 1) / (sqrt(Pi)*n^(3/2)). LINKS Vaclav Kotesovec, Table of n, a(n) for n = 1..224 FORMULA Equals limit_{n->infinity} A307210(n) / A324426(n). EXAMPLE 3.50478299933972837589112057043806125583893247862712753541994626614058385... MATHEMATICA (* The iteration cycle: *) \$MaxExtraPrecision = 1000; funs[n_] := Product[1 + 1/(i^3 + j^3), {i, 1, n}, {j, 1, n}]; Do[Print[N[Sum[(-1)^(m + j)*funs[j*Floor[200/m]] * j^(m - 1)/(j - 1)!/(m - j)!, {j, 1, m}], 100]], {m, 10, 100, 10}] PROG (PARI) default(realprecision, 50); exp(sumalt(k=1, -(-1)^k/k*sumnum(i=1, sumnum(j=1, 1/(i^3+j^3)^k)))) \\ 15 decimals correct CROSSREFS Cf. A073017, A307210, A307215, A324403, A324426, A324443. Sequence in context: A102575 A200520 A224933 * A243967 A144541 A100609 Adjacent sequences:  A307206 A307207 A307208 * A307210 A307211 A307212 KEYWORD nonn,cons AUTHOR Vaclav Kotesovec, Mar 28 2019 STATUS approved

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Last modified June 20 09:12 EDT 2019. Contains 324234 sequences. (Running on oeis4.)