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A054010 Numbers n with property that n is divisible by the number of its proper divisors. 4
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 (list; graph; refs; listen; history; text; internal format)
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 (asher.auel(AT)reed.edu), Jan 12 2000

STATUS

approved

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Last modified September 21 17:46 EDT 2019. Contains 327273 sequences. (Running on oeis4.)