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!)
 A154895 Perfect numbers whose number of proper divisors is prime. 0
 6, 28, 8128, 137438691328, 2305843008139952128 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The next term is too large to include in the data section. If there are no odd perfect numbers then the next term is a(6) = 2^606 * (2^607 - 1) = 1.410... * 10^365. - Amiram Eldar, Jul 29 2020 LINKS FORMULA a(n) = A006516(A172461(n)), assuming that odd perfect numbers do not exist. - Amiram Eldar, Jul 29 2020 EXAMPLE 28 is member because the number of proper divisors of 28 is 5, a prime number. MATHEMATICA Table[2^(p-1)*(2^p-1), {p, Select[MersennePrimeExponent[Range[8]], PrimeQ[2# - 1] &]}] (* Amiram Eldar, Jul 29 2020 *) CROSSREFS Cf. A000396, A006516, A032741, A133033, A154896, A172461. Sequence in context: A038182 A095723 A057246 * A330163 A276493 A074849 Adjacent sequences:  A154892 A154893 A154894 * A154896 A154897 A154898 KEYWORD nonn AUTHOR Omar E. Pol, Jan 25 2009 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 25 18:51 EDT 2021. Contains 347659 sequences. (Running on oeis4.)