The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A219545 Integer values of sigma(n)/n that are prime. 3
 2, 2, 3, 2, 3, 2, 3, 2, 3, 3, 2, 5, 5, 3, 2, 5, 5, 5, 5, 5, 5, 2, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 2, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 2, 5, 7, 2, 5, 5, 7, 5, 5, 5, 7, 7, 7, 7, 5, 5, 7, 7, 7, 7, 5, 7, 7, 7, 7, 7, 7, 7, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A054030 consisting of primes among the abundancies sigma(m)/m of multiply perfect numbers m (see A007691). Each 2 corresponds to a perfect number A000396, so if there are infinitely many perfect numbers, then the sequence is infinite. If, in addition, there are only finitely many multiply perfect numbers m with sigma(m)/m > 2 (see A134639), then a(n) = 2 for all n > some N. REFERENCES R. K. Guy, Unsolved Problems in Number Theory, B2. LINKS A. Flammenkamp, The Multiply Perfect Numbers Page FORMULA a(n) = sigma(A065997(n))/A065997(n). EXAMPLE A065997(1) = 6 and sigma(6)/6 = (1+2+3+6)/6 = 2, so a(1) = 2. CROSSREFS Cf. A000396, A007691, A054030, A065997, A134639. Sequence in context: A276856 A174296 A163178 * A029374 A255933 A319396 Adjacent sequences:  A219542 A219543 A219544 * A219546 A219547 A219548 KEYWORD nonn AUTHOR Jonathan Sondow, Nov 22 2012 EXTENSIONS Extended by T. D. Noe, Nov 27 2012 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 September 22 22:24 EDT 2020. Contains 337291 sequences. (Running on oeis4.)