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 A372638 #17 May 10 2024 08:49:47
%S A372638 1,2,4,6,10,12,19,23,29,33,43,47,59,66,74,82,98,104,122,130,144,154,
%T A372638 176,184,204,216,234,248,276,284,314,330,350,366,394,406,442,460,484,
%U A372638 500,540,554,596,616,640,662,708,724,773,793,825,849,901,919,959,987,1023
%N A372638 a(n) = (1/6) * Sum_{k=1..n} phi(7*k).
%H A372638 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%F A372638 a(n) ~ (49/(16*Pi^2)) * n^2. - _Amiram Eldar_, May 08 2024
%t A372638 Accumulate[Table[EulerPhi[7*n], {n, 1, 60}]]/6 (* _Amiram Eldar_, May 08 2024 *)
%o A372638 (PARI) a(n) = sum(k=1, n, eulerphi(7*k))/6;
%Y A372638 Column k=7 of A372619.
%Y A372638 Partial sums of A359102.
%Y A372638 Cf. A000010.
%K A372638 nonn
%O A372638 1,2
%A A372638 _Seiichi Manyama_, May 08 2024