A054023 Chowla function of n is not divisible by the number of divisors of n.

4, 6, 8, 10, 12, 14, 16, 18, 20, 21, 22, 24, 25, 26, 28, 30, 33, 34, 38, 40, 42, 44, 45, 46, 48, 49, 52, 54, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 76, 77, 78, 80, 81, 82, 84, 85, 86, 88, 90, 92, 93, 94, 96, 99, 100, 102, 104, 105, 106, 108, 110, 112, 114

Offset: 1

Author

Asher Auel, Jan 19 2000

Keywords

• nonn

Comments

Chowla's function (A048050) = sum of divisors of n except 1 and n.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Complement is A054022.

Cf. A000005, A048050, A054014.

Programs

Maple

with(numtheory):
[seq(`if`((sigma(i)-i-1) mod tau(i) <> 0,i,print( )),i=1..1000)];

Mathematica

cfQ[n_]:=!Divisible[DivisorSigma[1,n]-1-n,DivisorSigma[0,n]]; Select[ Range[ 150],cfQ] (* Harvey P. Dale, Jul 22 2014 *)