A054021 - OEIS

A054021

Numbers n such that Chowla's function of n is divisible by the number of proper divisors of n.

2, 3, 4, 5, 7, 8, 11, 12, 13, 14, 17, 18, 19, 23, 24, 26, 27, 29, 31, 32, 35, 37, 38, 40, 41, 43, 47, 52, 53, 56, 59, 61, 62, 63, 65, 66, 67, 71, 73, 74, 77, 79, 83, 86, 88, 89, 90, 92, 95, 97, 101, 103, 104, 107, 109, 110, 112, 113, 119, 122, 125, 127, 128, 131, 134, 136

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

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

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MAPLE

with(numtheory):

[seq(`if`((sigma(i)-i-1) mod (tau(i)-1)=0, i, print( )), i=2..1000)];

MATHEMATICA

Select[Range[2, 150], Divisible[DivisorSigma[1, #]-1-#, DivisorSigma[ 0, #]-1]&] (* Harvey P. Dale, Aug 13 2018 *)