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 A372637 #13 Feb 16 2025 08:34:06
%S A372637 1,3,6,10,14,20,26,34,43,51,61,73,85,97,109,125,141,159,177,193,211,
%T A372637 231,253,277,297,321,348,372,400,424,454,486,516,548,572,608,644,680,
%U A372637 716,748,788,824,866,906,942,986,1032,1080,1122,1162,1210,1258,1310,1364,1404
%N A372637 a(n) = (1/2) * Sum_{k=1..n} phi(6*k).
%H A372637 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%F A372637 a(n) ~ (9/(2*Pi^2)) * n^2. - _Amiram Eldar_, May 08 2024
%t A372637 Accumulate[Table[EulerPhi[6*n], {n, 1, 60}]]/2 (* _Amiram Eldar_, May 08 2024 *)
%o A372637 (PARI) a(n) = sum(k=1, n, eulerphi(6*k))/2;
%Y A372637 Column k=6 of A372619.
%Y A372637 Cf. A000010.
%K A372637 nonn
%O A372637 1,2
%A A372637 _Seiichi Manyama_, May 08 2024