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 A164876 #11 Jun 02 2025 01:53:14
%S A164876 0,1,2,12,28,32,52,90,124,172,324,364,612,640,756,844,912,964,1476,
%T A164876 2052,2484,3492,4356,4644,4804,6372,7620,8164,10116,11556,16452,20196,
%U A164876 22212,26532,28980,33732,39780,41796,44676,55332,60516,63972,75204,82692
%N A164876 Record differences for n^2 - phi(n)*sigma(n).
%C A164876 These are the largest differences between n^2 and sigma(n)*phi(n).
%C A164876 All of the differences are in A069249.
%H A164876 Amiram Eldar, <a href="/A164876/b164876.txt">Table of n, a(n) for n = 1..10000</a>
%F A164876 a(n) = A069249(A164875(n)). - _Amiram Eldar_, Aug 29 2019
%e A164876 sigma(10) = 18; phi(10) = 4; 10^2 - sigma(10)*phi(10) = 28. This difference, 28, exceeds the difference for every smaller n, so 28 is in this sequence and 10 is in A164875.
%t A164876 f[n_] := n^2 - EulerPhi[n] * DivisorSigma[1, n]; s = {}; fm = -1; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, fm]], {n, 1, 500}]; s (* _Amiram Eldar_, Aug 29 2019 *)
%Y A164876 Cf. A069249, A164875, A000203, A000010.
%K A164876 nonn
%O A164876 1,3
%A A164876 _Walter Nissen_, Aug 29 2009
%E A164876 a(1) = 0 added by _Amiram Eldar_, Aug 29 2019