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 A181540 #21 Jul 12 2020 10:18:46
%S A181540 0,1,3,8,13,26,29,54,59,84,93,142,139,202,195,244,259,352,327,444,433,
%T A181540 508,505,656,639,776,719,866,889,1054,1057,1208,1151,1332,1255,1624,
%U A181540 1575,1728,1579,1886,2011,2130,2159,2348,2329,2716,2329
%N A181540 a(n) = Sum_{k=0..n} gcd(n,k)*phi(k).
%C A181540 Row sums of triangle A181538.
%p A181540 A181540 := n -> add(igcd(n,k)*numtheory[phi](k),k=0..n);
%t A181540 Table[Sum[GCD[n,k]EulerPhi[k],{k,0,n}],{n,0,50}] (* _Harvey P. Dale_, Jul 12 2020 *)
%o A181540 (PARI) a(n) = sum(k=1, n, gcd(n, k)*eulerphi(k)); \\ _Michel Marcus_, May 18 2018
%Y A181540 Cf. A181538.
%K A181540 nonn
%O A181540 0,3
%A A181540 _Peter Luschny_, Oct 29 2010