A054010 Numbers n with property that n is divisible by the number of its proper divisors.

2, 3, 4, 5, 6, 7, 11, 13, 15, 16, 17, 19, 20, 21, 23, 27, 29, 31, 33, 37, 39, 41, 42, 43, 45, 47, 50, 51, 53, 56, 57, 59, 61, 67, 69, 70, 71, 73, 75, 79, 83, 87, 89, 93, 97, 101, 103, 105, 107, 109, 111, 113, 120, 123, 127, 129, 131, 132, 137, 139, 141, 149, 151, 154

Offset

1,1

Comments

All primes are in this sequence, having only one proper divisor. The specifically nonprime members of this sequence are in A055719. - Carl R. White, Jul 11 2012

Links

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

Formula

Numbers n such that A054009(n) = 0.

Example

There are three proper divisors of 6, {1, 2, 3}, 6 is divisible by 3.

Maple

[seq(`if`(i mod (tau(i)-1) = 0, i, print( )), i=2..190)];

Mathematica

Select[Range[2, 100], IntegerQ[ #/(-1+DivisorSigma[0, # ])]&] (* Wouter Meeussen, Jun 07 2005 *)

Crossrefs

Cf. A032741, A033950, A054009, A055719.

Sequence in context: A280536 A090563 A045745 * A051948 A193461 A192587

Adjacent sequences: A054007 A054008 A054009 * A054011 A054012 A054013

Keyword

nonn

Author

Asher Auel, Jan 12 2000

Status

approved