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 A062972 #17 Dec 01 2019 07:16:11 %S A062972 1,2,3,4,5,7,11,13,15,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79, %T A062972 83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173, %U A062972 179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269 %N A062972 Numbers k such that the Chowla function of k is divisible by phi(k). %C A062972 Chowla's function (A048050) = sum of divisors of n except 1 and n. %C A062972 Sequence contains all primes; see A070037 for nonprime terms. - _Charles R Greathouse IV_, Apr 14 2010 %H A062972 Amiram Eldar, <a href="/A062972/b062972.txt">Table of n, a(n) for n = 1..10000</a> %t A062972 chowla[1] = 0; chowla[n_] := DivisorSigma[1, n] - n - 1; Select[Range[270], Divisible[chowla[#], EulerPhi[#]] &] (* _Amiram Eldar_, Dec 01 2019 *) %o A062972 (PARI) j=[]; for(n=1,600, if(Mod(sigma(n)-n-1,eulerphi(n)) == 0,j=concat(j,n))); j %Y A062972 Cf. A000010, A048050, A070037. %K A062972 nonn %O A062972 1,2 %A A062972 _Jason Earls_, Jul 24 2001