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 A062973 #9 Dec 15 2017 17:35:18 %S A062973 6,8,9,10,12,14,16,18,20,21,22,24,25,26,27,28,30,32,33,34,35,36,38,39, %T A062973 40,42,44,45,46,48,49,50,51,52,54,55,56,57,58,60,62,63,64,65,66,68,69, %U A062973 70,72,74,75,76,77,78,80,81,82,84,85,86,87,88,90,91,92,93,94,95,96,98 %N A062973 Chowla function of n is not divisible by phi(n). %C A062973 Chowla's function (A048050) = sum of divisors of n except 1 and n. %t A062973 okcfQ[n_]:=!Divisible[DivisorSigma[1,n]-n-1,EulerPhi[n]] %t A062973 Select[Range[100],okcfQ] (* _Harvey P. Dale_, Feb 25 2011 *) %o A062973 (PARI) j=[]; for(n=1,400, if(Mod(sigma(n)-n-1,eulerphi(n))!=0,j=concat(j,n))); j %K A062973 nonn %O A062973 1,1 %A A062973 _Jason Earls_, Jul 24 2001