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.

User: Rory Glover

Rory Glover's wiki page.

Rory Glover has authored 1 sequences.

A255429 Numbers with a prime number of nontrivial divisors.

Original entry on oeis.org

6, 8, 10, 14, 15, 16, 21, 22, 26, 27, 33, 34, 35, 36, 38, 39, 46, 51, 55, 57, 58, 62, 64, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 100, 106, 111, 115, 118, 119, 122, 123, 125, 129, 133, 134, 141, 142, 143, 144, 145, 146, 155, 158, 159, 161, 166, 177, 178, 183, 185, 187, 194, 196
Offset: 1

Views

Author

Rory Glover, Feb 22 2015

Keywords

Comments

Empirically, numbers in this sequence seem to have few divisors.
This sequence appears to be the union of A130763 and the squares of A225649. - Kellen Myers, Apr 21 2015

Crossrefs

Cf. A063806, A070824, A130763, A225649.

Programs

  • Magma
    [n: n in [1..200] | IsPrime(NumberOfDivisors(n)-2)]; // Vincenzo Librandi, Apr 21 2015
  • Mathematica
    seq[n_] := Select[Range[n], PrimeQ[DivisorSigma[0, #] - 2] &] (* Kellen Myers, Apr 21 2015 *)
  • PARI
    isok(m) = isprime(numdiv(m)-1); \\ Michel Marcus, Jan 13 2023

Formula

{n: A070824(n) in A000040}.

Extensions

Terms fixed by Kellen Myers, Apr 21 2015
Name corrected by Michel Marcus, Jan 13 2023

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement.