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 A383717 #13 May 07 2025 08:17:40
%S A383717 1,2,3,2,5,6,7,0,3,10,11,6,13,14,15,0,17,6,19,10,21,22,23,0,5,26,0,14,
%T A383717 29,30,31,0,33,34,35,6,37,38,39,0,41,42,43,22,15,46,47,0,7,10,51,26,
%U A383717 53,0,55,0,57,58,59,30,61,62,21,0,65,66,67,34,69,70,71,0,73
%N A383717 Dirichlet g.f.: Product_{p prime} (1 + 1/p^(s-1) + 1/p^(2*s-1)).
%H A383717 Vaclav Kotesovec, <a href="/A383717/b383717.txt">Table of n, a(n) for n = 1..10000</a>
%F A383717 Sum_{k=1..n} a(k) ~ c * n^2/2, where c = Product_{p prime} (1 - 1/p^2 + 1/p^3 - 1/p^4) = 0.684286924186862318141968725791218083472312736723163777284618226290055...
%F A383717 Multiplicative with a(p^e) = p is e <= 2, and 0 otherwise. - _Amiram Eldar_, May 07 2025
%t A383717 f[p_, e_] := If[e < 3, p, 0]; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, May 07 2025 *)
%o A383717 (PARI) for(n=1, 100, print1(direuler(p=2, n, (1 + X*p + X^2*p))[n], ", "))
%Y A383717 Cf. A007947, A056552, A335341, A336649.
%K A383717 nonn,mult,easy
%O A383717 1,2
%A A383717 _Vaclav Kotesovec_, May 07 2025