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A028260
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Numbers n such that number of prime divisors of n (counted with multiplicity) is even; Liouville function lambda(n) (A008836) is positive.
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18
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1, 4, 6, 9, 10, 14, 15, 16, 21, 22, 24, 25, 26, 33, 34, 35, 36, 38, 39, 40, 46, 49, 51, 54, 55, 56, 57, 58, 60, 62, 64, 65, 69, 74, 77, 81, 82, 84, 85, 86, 87, 88, 90, 91, 93, 94, 95, 96, 100, 104, 106, 111, 115, 118, 119, 121, 122, 123, 126, 129, 132, 133, 134
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| If n appears, p*n does not (p primes) . - Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Jun 10 2006
The product of any two members of the this sequence, or any two members of the complement of this sequence (A026424) is a member of this sequence. The product of a member of this sequence and a member of A026424 is a member of A026424. The primitive elements of this sequence are the semiprimes (A001358). - Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Nov 27 2006
A072978 is a subsequence. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 20 2008]
A066829(a(n)) = 0. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jun 26 2009]
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..10000
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FORMULA
| A001222(a(n)) mod 2 = 0. [Reinhard Zumkeller, Oct 05 2011]
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MAPLE
| with(numtheory); A028260 := proc(n) option remember: local k: if(n=1)then return 1: fi: for k from procname(n-1)+1 do if(bigomega(k) mod 2=0)then return k: fi: od: end: seq(A028260(n), n=1..63); # Nathaniel Johnston, May 27 2011
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MATHEMATICA
| Select[Range[200], EvenQ[PrimeOmega[#]]&] (* From Harvey P. Dale, Aug 14 2011 *)
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PROG
| (Haskell)
a028260 n = a028260_list !! (n-1)
a028260_list = filter (even . a001222) [1..]
-- Reinhard Zumkeller, Oct 05 2011
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CROSSREFS
| Cf. A001222, A001358, A008836, A026424 (complement).
Cf. A145784. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Oct 19 2008]
Sequence in context: A189167 A010428 A189300 * A085155 A063762 A001358
Adjacent sequences: A028257 A028258 A028259 * A028261 A028262 A028263
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KEYWORD
| nonn,easy,nice
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AUTHOR
| Dan Asimov (dan(AT)research.att.com)
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