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 A054023 #13 Oct 27 2023 22:00:46 %S A054023 4,6,8,10,12,14,16,18,20,21,22,24,25,26,28,30,33,34,38,40,42,44,45,46, %T A054023 48,49,52,54,56,57,58,60,62,63,64,65,66,68,69,70,72,74,76,77,78,80,81, %U A054023 82,84,85,86,88,90,92,93,94,96,99,100,102,104,105,106,108,110,112,114 %N A054023 Chowla function of n is not divisible by the number of divisors of n. %C A054023 Chowla's function (A048050) = sum of divisors of n except 1 and n. %H A054023 Vincenzo Librandi, <a href="/A054023/b054023.txt">Table of n, a(n) for n = 1..1000</a> %p A054023 with(numtheory): %p A054023 [seq(`if`((sigma(i)-i-1) mod tau(i) <> 0,i,print( )),i=1..1000)]; %t A054023 cfQ[n_]:=!Divisible[DivisorSigma[1,n]-1-n,DivisorSigma[0,n]]; Select[ Range[ 150],cfQ] (* _Harvey P. Dale_, Jul 22 2014 *) %Y A054023 Complement is A054022. %Y A054023 Cf. A000005, A048050, A054014. %K A054023 nonn %O A054023 1,1 %A A054023 _Asher Auel_, Jan 19 2000