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Search: id:A066715
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| A066715 |
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GCD of 2n+1 and sigma(2n+1). |
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+0
5
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| 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 7, 1, 5, 1, 3, 1, 1, 3, 1, 1, 1, 1, 1, 13, 1, 1, 3, 1, 1, 1, 1, 1, 15, 1, 1, 3, 1, 5, 3, 1, 1, 9, 1, 1, 3, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3
(list; graph; listen)
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OFFSET
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0,8
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COMMENT
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If gcd(n, sigma(n))=1 then n is an odd perfect number. It seems however that gcd(n, sigma(n)) is always significantly less than n.
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EXAMPLE
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a(5) = 1 as gcd(5,6) = 1. a(15) = gcd(15, sigma(15)) = gcd(15,(1+3+5+15)) = gcd(15,24) = 3
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PROGRAM
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(PARI) forstep (x=3, 2000, 2, write1("oddperfectgcd.txt", gcd(sigma(x), x), ", "))
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CROSSREFS
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Adjacent sequences: A066712 A066713 A066714 this_sequence A066716 A066717 A066718
Sequence in context: A031244 A030576 A101874 this_sequence A082457 A031178 A091407
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KEYWORD
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nonn
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AUTHOR
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Jon Perry (perry(AT)globalnet.co.uk), Jan 14 2002
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