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 A239274 #11 Jul 14 2021 10:03:59 %S A239274 1,88,1104,492624,30818736,200827760,1598249556,4575586644,8491046375, %T A239274 8554970196,29917317500,54481242640,202195886375,3201891498000 %N A239274 Numbers k such that k' = sigma(k) - phi(k), where k' = A003415(k) is the arithmetic derivative of k. %C A239274 a(15) > 10^13. %t A239274 ad[1]=0; ad[n_]:=n*Total[(#1[[2]] / #1[[1]]&) /@ FactorInteger[n]]; Select[Range[500000], ad[#] == DivisorSigma[1,#] - EulerPhi[#] &] %Y A239274 Cf. A000010, A000203, A003415, A166374, A230164. %K A239274 nonn %O A239274 1,2 %A A239274 _Giovanni Resta_, Mar 13 2014