

A158338


Composite numbers k such that k  number of divisors of k = prime.


1



6, 15, 16, 21, 27, 33, 35, 51, 57, 65, 77, 87, 93, 105, 111, 135, 141, 143, 155, 161, 165, 177, 183, 185, 189, 201, 203, 215, 231, 237, 245, 267, 275, 285, 287, 321, 335, 341, 345, 357, 371, 375, 377, 393, 413, 425, 429, 437, 447, 453, 465, 471
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OFFSET

1,1


COMMENTS

Subsequence of A067531.  Michel Marcus, Dec 22 2014


LINKS

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


EXAMPLE

6 is composite and has 4 divisors (1, 2, 3, 6); 6  4 = 2, which is prime, so 6 is in the sequence.
15 is composite and has 4 divisors (1, 3, 5, 15); 15  4 = 11, which is prime, so 15 is in the sequence.
16 is composite and has 5 divisors (1, 2, 4, 8, 16); 16  5 = 11, which is prime, so 16 is in the sequence.


MATHEMATICA

Select[Range[500], CompositeQ[#] && PrimeQ[#  DivisorSigma[0, #]] &] (* Amiram Eldar, Jul 16 2019 *)


PROG

(MAGMA) [k:k in [1..500]not IsPrime(k) and IsPrime(k#Divisors(k))]; // Marius A. Burtea, Jul 16 2019


CROSSREFS

Cf. A000005, A000040, A002808, A035004, A067531.
Sequence in context: A199094 A009579 A114812 * A139204 A122661 A133481
Adjacent sequences: A158335 A158336 A158337 * A158339 A158340 A158341


KEYWORD

nonn


AUTHOR

JuriStepan Gerasimov, Mar 16 2009, Nov 14 2009


EXTENSIONS

Extended by R. J. Mathar, May 19 2010


STATUS

approved



