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 A248815 #13 Jul 11 2019 17:48:47 %S A248815 31,32,80,81,112,176,192,244,368,752,859,912,944,1296,1328,1712,1723, %T A248815 2672,2864,3024,3632,4208,5552,5744,6128,6156,7472,7664,8048,8748, %U A248815 9008,9392,11504,13424,13808,14192,15728,16304,18992,20412,20528,20912,21104,21872 %N A248815 Numbers equal to the arithmetic derivative of their Euler totient function. %C A248815 Solutions of the equation n = (phi(n))’. %H A248815 Amiram Eldar, <a href="/A248815/b248815.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..500 from Paolo P. Lava) %e A248815 Euler totient function of 32 is 16 and the arithmetic derivative of 16 is 32. %p A248815 with(numtheory): P:= proc(q) local a,n,p; for n from 1 to q do %p A248815 a:=phi(n)*add(op(2,p)/op(1,p),p=ifactors(phi(n))[2]); %p A248815 if n=a then print(n); fi; od; end: P(10^9); %t A248815 deriv[n_] := n*Total[#2/#1 & @@@ FactorInteger[n]]; aQ[1] = 1; aQ[n_] := deriv[EulerPhi[n]] == n; Select[Range[25000], aQ] (* _Amiram Eldar_, Jul 11 2019 *) %Y A248815 Cf. A000005, A003415, A166374. %K A248815 nonn %O A248815 1,1 %A A248815 _Paolo P. Lava_, Oct 15 2014