A075818 Even numbers with exactly 3 prime factors (counted with multiplicity).
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
Offset: 1
Examples
28=2^2*7, 30=2*3*5 and 42=2*3*7 are even and are products of exactly 3 primes.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..2626
Programs
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Magma
[2*n: n in [2..200] | &+[d[2]: d in Factorization(n)] eq 2]; // Vincenzo Librandi Nov 10 2018
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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;
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Mathematica
Select[Range[100], Plus@@Last/@FactorInteger[#]==2&] 2 (* Vincenzo Librandi, Nov 10 2018 *) Select[Range[2,400,2],PrimeOmega[#]==3&] (* Harvey P. Dale, Oct 15 2021 *)
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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
Formula
a(n)=2*A001358(n). - Juri-Stepan Gerasimov, Jun 01 2010
Extensions
Edited by Dean Hickerson, Oct 21 2002
Comments