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 A372635 #16 Feb 16 2025 08:34:06
%S A372635 1,4,16,36,100,144,324,484,784,1024,1764,2116,3364,4096,5184,6400,
%T A372635 9216,10404,14400,16384,19600,22500,29584,32400,40000,44944,52900,
%U A372635 58564,72900,77284,94864,104976,118336,129600,147456,156816,186624,202500,224676,240100,280900
%N A372635 a(n) = Sum_{j=1..n} Sum_{k=1..n} phi(j)*phi(k).
%H A372635 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientFunction.html">Totient Function</a>.
%F A372635 a(n) = A002088(n)^2.
%F A372635 a(n) ~ 9*n^4/(Pi^4). - _Vaclav Kotesovec_, May 08 2024
%t A372635 nmax = 50; Accumulate[Table[EulerPhi[j], {j, 1, nmax}]]^2 (* _Vaclav Kotesovec_, May 08 2024 *)
%o A372635 (PARI) a(n) = sum(j=1, n, sum(k=1, n, eulerphi(j)*eulerphi(k)));
%o A372635 (PARI) a(n) = sum(k=1, n, eulerphi(k))^2;
%Y A372635 Cf. A000010, A002088, A372633.
%K A372635 nonn
%O A372635 1,2
%A A372635 _Seiichi Manyama_, May 08 2024