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 A372622 #14 Feb 16 2025 08:34:06
%S A372622 1,2,4,6,11,13,19,23,29,34,44,48,60,66,76,84,100,106,124,134,146,156,
%T A372622 178,186,211,223,241,253,281,291,321,337,357,373,403,415,451,469,493,
%U A372622 513,553,565,607,627,657,679,725,741,783,808,840,864,916,934,984,1008,1044
%N A372622 a(n) = (1/4) * Sum_{k=1..n} phi(5*k).
%H A372622 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%F A372622 a(n) ~ (25/(8*Pi^2)) * n^2. - _Amiram Eldar_, May 08 2024
%t A372622 Accumulate[Table[EulerPhi[5*n], {n, 1, 60}]]/4 (* _Amiram Eldar_, May 08 2024 *)
%o A372622 (PARI) a(n) = sum(k=1, n, eulerphi(5*k))/4;
%Y A372622 Partial sums of A359101.
%Y A372622 Column k=5 of A372619.
%Y A372622 Cf. A000010.
%K A372622 nonn
%O A372622 1,2
%A A372622 _Seiichi Manyama_, May 07 2024