A055719 d(n)-1 | n and n is not prime.

4, 6, 15, 16, 20, 21, 27, 33, 39, 42, 45, 50, 51, 56, 57, 69, 70, 75, 87, 93, 105, 111, 120, 123, 129, 132, 141, 154, 159, 162, 175, 177, 182, 183, 189, 198, 201, 210, 213, 219, 220, 231, 237, 238, 245, 249, 256, 266, 267, 270, 273, 275, 291, 303, 308, 309, 321

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Comments

Composite integers divisible by 1 less than the number of their divisors.

This is, composite members of A054010. - Carl R. White, Jul 11 2012

Links

• Carl R. White, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A054010.

Programs

Mathematica

Do[ If[ !PrimeQ[ n ], If[ IntegerQ[ n/(DivisorSigma[ 0, n ]-1) ], Print[ n ] ] ], {n, 1, 500} ]
Select[Range[2,400],!PrimeQ[#]&&Divisible[#,DivisorSigma[0,#]-1]&] (* Harvey P. Dale, Mar 13 2013 *)