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 A164875 #11 Jun 02 2025 01:53:06
%S A164875 1,2,4,6,10,12,14,18,22,26,30,38,42,50,54,58,60,62,66,78,90,102,114,
%T A164875 126,130,138,150,170,174,186,210,246,258,282,294,318,330,354,366,390,
%U A164875 426,438,462,498,510,534,546,570,606,618,642,654,678,690,714,750,762,786
%N A164875 Record holders for n^2 - phi(n)*sigma(n).
%C A164875 These numbers exhibit the largest differences between n^2 and sigma(n)*phi(n).
%C A164875 All of the differences are in A069249, and are guaranteed to be positive by Th. 329 in Hardy & Wright. The record differences are in A164876.
%H A164875 Amiram Eldar, <a href="/A164875/b164875.txt">Table of n, a(n) for n = 1..10000</a>
%e A164875 sigma(10) = 18; phi(10) = 4; 10^2 - sigma(10)*phi(10) = 28. This difference, 28, exceeds the difference for every smaller n, so 10 is in this sequence and 28 is in A164876.
%t A164875 f[n_] := n^2 - EulerPhi[n] * DivisorSigma[1, n]; s = {}; fm = -1; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, n]], {n, 1, 786}]; s (* _Amiram Eldar_, Aug 29 2019 *)
%Y A164875 Cf. A069249, A164876, A000203, A000010.
%K A164875 nonn
%O A164875 1,2
%A A164875 _Walter Nissen_, Aug 29 2009