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Search: id:A139710
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| A139710 |
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A number n is included if the sum of (the largest divisor of n that is <= sqrt(n)) and (the smallest divisor of n that is >= sqrt(n)) is odd. |
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2
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| 2, 6, 10, 12, 14, 18, 20, 22, 26, 28, 30, 34, 38, 40, 42, 44, 46, 50, 52, 54, 56, 58, 62, 66, 68, 70, 72, 74, 76, 78, 82, 84, 86, 88, 90, 92, 94, 98, 102, 104, 106, 108, 110, 114, 116, 118, 122, 124, 126, 130, 132, 134, 136, 138, 142, 146, 148, 150, 152, 154, 156, 158
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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All terms of this sequence are even.
A139711 contains all positive integers not in this sequence, and vice versa.
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FORMULA
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{n: A000035(A033676(n)+A033677(n))=1}. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 11 2008
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EXAMPLE
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The divisors of 12 are 1,2,3,4,6,12. The middle 2 divisors are 3 and 4. The sum of these is 7, which is odd. So 12 is included in the sequence.
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MAPLE
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A033676 := proc(n) local d ; for d from floor(sqrt(n)) to 1 by -1 do if n mod d = 0 then RETURN(d) ; fi ; od: end: A033677 := proc(n) n/A033676(n) ; end: isA139710 := proc(n) RETURN ( ( A033676(n)+A033677(n) ) mod 2 = 1 ) ; end: for n from 1 to 300 do if isA139710(n) then printf("%d, ", n) ; fi ; od: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 11 2008
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CROSSREFS
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Cf. A063655, A139711.
Adjacent sequences: A139707 A139708 A139709 this_sequence A139711 A139712 A139713
Sequence in context: A133520 A099017 A139799 this_sequence A057921 A095300 A097381
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Apr 30 2008
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 11 2008
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