A158337 Composite numbers k such that k - (number of prime factors of k, counted with multiplicity) is a prime.

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

Offset

1,1

Links

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

Example

4 is a term: 4 = 2*2 has 2 prime factors (counted with multiplicity), and 4 - 2 = 2 (a prime).
8 is a term: 8 = 2*2*2 has 3 prime factors, and 8 - 3 - 5 (a prime).
9 is a term: 9 = 3*3 has 2 prime factors, and 9 - 2 = 7 (a prime).

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: A336663 A329936 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