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Search: id:A026424
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| A026424 |
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Number of prime divisors (counted with multiplicity) is odd; Liouville function lambda(n) (A008836) is negative. |
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+0
16
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| 2, 3, 5, 7, 8, 11, 12, 13, 17, 18, 19, 20, 23, 27, 28, 29, 30, 31, 32, 37, 41, 42, 43, 44, 45, 47, 48, 50, 52, 53, 59, 61, 63, 66, 67, 68, 70, 71, 72, 73, 75, 76, 78, 79, 80, 83, 89, 92, 97, 98, 99, 101, 102, 103, 105, 107, 108, 109, 110, 112
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Neither this sequence nor its complement (A028260) contains any infinite arithmetic progression. [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Sep 05 2008]
A066829(a(n)) = 1. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jun 26 2009]
These numbers can be generated by the sieving process described in A066829. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jul 01 2009]
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REFERENCES
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S. Ramanujan, Irregular numbers, J. Indian Math. Soc., 5 (1913), 105-106; Coll. Papers 20-21.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
S. Ramanujan, Irregular numbers
Eric Weisstein's World of Mathematics, Prime Sums
Index entries for sequences generated by sieves [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jul 01 2009]
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FORMULA
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Sum 1/a(n)^m = (zeta(m)^2-zeta(2m))/(2*zeta(m)). - Ramanujan.
n>=2 is in sequence if n is not the product of two smaller elements. - David W. Wilson (davidwwilson(AT)comcast.net), May 06 2005
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CROSSREFS
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Cf. A008836, A028260.
Apart from initial term, same as A026422.
Sequence in context: A100959 A166982 A026422 this_sequence A141832 A066680 A028780
Adjacent sequences: A026421 A026422 A026423 this_sequence A026425 A026426 A026427
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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