This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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