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