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A158337 Composite numbers k such that k - number of prime factors of k = prime. 1
4, 8, 9, 15, 20, 21, 25, 33, 39, 44, 48, 49, 50, 55, 69, 70, 72, 76, 85, 91, 92, 108, 110, 111, 112, 115, 116, 129, 130, 133, 135, 141, 154, 159, 162, 168, 169, 170, 182, 183, 201, 213, 230, 235, 236, 242, 244, 253, 259, 265, 266, 284, 286, 288, 295, 297, 309 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

If composite=4=2*2 and 4-2=2=prime, then 4=a(1). If composite=8=2*2*2 and 8-3=5=prime, then 8=a(2). If composite=9=3*3 and 9-2=7=prime, then 9=a(3), etc.

MAPLE

select(t -> not isprime(t) and isprime(t - numtheory:-bigomega(t)), [$4..1000]); # Robert Israel, Apr 08 2018

MATHEMATICA

Select[Range[350], CompositeQ[#]&&PrimeQ[#-PrimeOmega[#]]&] (* Harvey P. Dale, Apr 01 2019 *)

CROSSREFS

Cf. A000040, A002808, A069345.

Sequence in context: A137055 A078177 A023886 * A161542 A131195 A020217

Adjacent sequences:  A158334 A158335 A158336 * A158338 A158339 A158340

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Mar 16 2009, Nov 14 2009

EXTENSIONS

Entries checked by R. J. Mathar, May 19 2010

STATUS

approved

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Last modified May 19 10:55 EDT 2019. Contains 323390 sequences. (Running on oeis4.)