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A075818 Even numbers with exactly 3 prime factors (counted with multiplicity). 8
8, 12, 18, 20, 28, 30, 42, 44, 50, 52, 66, 68, 70, 76, 78, 92, 98, 102, 110, 114, 116, 124, 130, 138, 148, 154, 164, 170, 172, 174, 182, 186, 188, 190, 212, 222, 230, 236, 238, 242, 244, 246, 258, 266, 268, 282, 284, 286, 290, 292, 310, 316, 318, 322, 332, 338 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Twice the semiprime numbers. - Juri-Stepan Gerasimov, Jun 01 2010

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..2626

FORMULA

a(n)=2*A001358(n). - Juri-Stepan Gerasimov, Jun 01 2010

EXAMPLE

28=2^2*7, 30=2*3*5 and 42=2*3*7 are even and are products of exactly 3 primes.

MAPLE

ts_bo3_sod := proc(n); if (numtheory[bigomega](n)=3 and type(n, even)='true') then RETURN(n); fi end: abo3sod := [seq(ts_bo3_sod(i), i=1..2300)]: abo3sod;

MATHEMATICA

Select[Range[100], Plus@@Last/@FactorInteger[#]==2&] 2 (* Vincenzo Librandi, Nov 10 2018 *)

PROG

(PARI) list(lim)=my(v=List()); forprime(p=2, lim\4, forprime(q=2, min(lim\p\2, p), listput(v, 2*p*q))); Set(v) \\ Charles R Greathouse IV, Aug 29 2017

(MAGMA) [2*n: n in [2..200] | &+[d[2]: d in Factorization(n)] eq 2]; // Vincenzo Librandi Nov 10 2018

CROSSREFS

Cf. A046470, A053858.

Sequence in context: A187042 A285508 A054397 * A090738 A085103 A280968

Adjacent sequences:  A075815 A075816 A075817 * A075819 A075820 A075821

KEYWORD

easy,nonn

AUTHOR

Jani Melik, Oct 13 2002

EXTENSIONS

Edited by Dean Hickerson, Oct 21 2002

STATUS

approved

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Last modified April 10 07:44 EDT 2021. Contains 342843 sequences. (Running on oeis4.)