A055719 - OEIS

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

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OFFSET

1,1

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

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 *)

CROSSREFS