A053858 Squarefree even composite numbers with an odd number of prime factors.

30, 42, 66, 70, 78, 102, 110, 114, 130, 138, 154, 170, 174, 182, 186, 190, 222, 230, 238, 246, 258, 266, 282, 286, 290, 310, 318, 322, 354, 366, 370, 374, 402, 406, 410, 418, 426, 430, 434, 438, 442, 470, 474, 494, 498, 506, 518, 530, 534, 574, 582, 590

Offset: 1

Author

Enoch Haga, Mar 28 2000

Keywords

• easy
• nonn

Comments

Prime factors counted with multiplicity. - Harvey P. Dale, May 21 2024

Examples

			a(3)=66 because 66 is even and its prime divisors are 2, 3 and 11, an odd number.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

A075819 is a subsequence. Intersection of A026424, A039956, and A002808.

Programs

Maple

ts_m2_sod := proc(n); if (numtheory[mobius](n)=-1 and isprime(n)='false' and type(n,even)='true') then RETURN(n); fi end: am2sod := [seq(ts_m2_sod(i), i=1..2500)]: am2sod;

Mathematica

Select[Range[2,602,2],CompositeQ[#]&&SquareFreeQ[#]&&OddQ[PrimeOmega[#]]&] (* Harvey P. Dale, May 21 2024 *)

PARI

is(n,f=factor(n))=n%2==0 && #f[,2]>2 && vecmax(f[,2])==1 && (#f[,2])%2 \\ Charles R Greathouse IV, Aug 29 2017

Extensions

Name corrected by Charles R Greathouse IV, Aug 29 2017