cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A154895 Perfect numbers whose number of proper divisors is prime.

Original entry on oeis.org

6, 28, 8128, 137438691328, 2305843008139952128
Offset: 1

Views

Author

Omar E. Pol, Jan 25 2009

Keywords

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

Examples

			28 is member because the number of proper divisors of 28 is 5, a prime number.

Crossrefs

Cf. A000396, A006516, A032741, A133033, A154896, A172461.

Programs

  • Mathematica
    Table[2^(p-1)*(2^p-1), {p, Select[MersennePrimeExponent[Range[8]], PrimeQ[2# - 1] &]}] (* Amiram Eldar, Jul 29 2020 *)

Formula

a(n) = A006516(A172461(n)), assuming that odd perfect numbers do not exist. - Amiram Eldar, Jul 29 2020
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