This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A279964 #25 Jan 07 2025 02:01:38
%S A279964 0,1,138,3377,39890,297550,1623980,7065329,25808790,82305816,
%T A279964 234756742,611706830,1474831246,3334313204,7118797268,14485772017,
%U A279964 28206850488,52921773667,95877425634,168644231672,288301373792,481166453010,784226941604,1253068878542,1962356045590
%N A279964 a(n) = Sum_{k=1..n-1} sigma_3(k)*sigma_7(n-k).
%H A279964 Seiichi Manyama, <a href="/A279964/b279964.txt">Table of n, a(n) for n = 1..1000</a>
%F A279964 36*tau(n) = 5*sigma_3(n) + 10*sigma_7(n) + 21*sigma_5(n) + 2400*a(n) - 5292*A279889(n).
%t A279964 Table[Sum[DivisorSigma[3, k] * DivisorSigma[7, n - k], {k, 1, n - 1}], {n, 1, 25}] (* _Indranil Ghosh_, Mar 12 2017 *)
%t A279964 a[n_] := (1800 * RamanujanTau[n] + 273 * DivisorSigma[11, n] - 1382 * DivisorSigma[7, n] - 691 * DivisorSigma[3, n]) / 331680; Array[a, 25] (* _Amiram Eldar_, Jan 07 2025 *)
%o A279964 (PARI) a(n) = sum(k=1, n-1, sigma(k, 3)*sigma(n-k,7)); \\ _Michel Marcus_, Dec 24 2016
%o A279964 (PARI) a(n) = {my(f = factor(n)); (1800 * ramanujantau(n) + 273 * sigma(f, 11) - 1382 * sigma(f, 7) - 691 * sigma(f, 3)) / 331680;} \\ _Amiram Eldar_, Jan 07 2025
%Y A279964 Cf. A000594, A001158, A001160, A013955, A279889.
%K A279964 nonn
%O A279964 1,3
%A A279964 _Seiichi Manyama_, Dec 23 2016