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A066715 a(n) = gcd(2n+1, sigma(2n+1)). 5
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; refs; listen; history; text; internal format)
OFFSET

0,8

COMMENTS

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.

LINKS

Harry J. Smith, Table of n, a(n) for n = 0..1000

EXAMPLE

a(5) = 1 as gcd(5,6) = 1. a(15) = gcd(15, sigma(15)) = gcd(15,(1+3+5+15)) = gcd(15,24) = 3.

PROG

(PARI) forstep (x=3, 2000, 2, write1("oddperfectgcd.txt", gcd(sigma(x), x), ", "))

(PARI) { for (n=0, 1000, write("b066715.txt", n, " ", gcd(2*n+1, sigma(2*n+1))) ) } \\ Harry J. Smith, Mar 19 2010

CROSSREFS

Sequence in context: A030576 A101874 A318449 * A082457 A031178 A091407

Adjacent sequences:  A066712 A066713 A066714 * A066716 A066717 A066718

KEYWORD

nonn

AUTHOR

Jon Perry, Jan 14 2002

STATUS

approved

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Last modified June 18 14:52 EDT 2019. Contains 324213 sequences. (Running on oeis4.)