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.

A141229 Odd numbers k for which A006694((k-1)/2) = 3.

Original entry on oeis.org

27, 43, 109, 125, 157, 229, 277, 283, 307, 499, 643, 691, 733, 739, 811, 997, 1021, 1051, 1069, 1093, 1331, 1459, 1579, 1597, 1627, 1699, 1723, 1789, 1933, 2179, 2197, 2203, 2251, 2341, 2347, 2749, 2917, 3163, 3181, 3229, 3259, 3373, 4027, 4339, 4549, 4597, 4651, 4909
Offset: 1

Views

Author

Vladimir Shevelev, Jun 15 2008

Keywords

Comments

Conjecture. The terms of the sequence have only one prime divisor; moreover, p^3 is in the sequence if and only if p is in A001122.

Crossrefs

Programs

  • Mathematica
    r[n_] := EulerPhi[n]/MultiplicativeOrder[2, n]; Select[Range[5000], Total@(r /@ Divisors[#]) - 1 == 3 &] (* Amiram Eldar, Sep 12 2019 *)
  • PARI
    a006694(n)=sumdiv(2*n+1, d, eulerphi(d)/znorder(Mod(2, d))) - 1;
    isok(n) = (n % 2) && (a006694((n-1)/2) == 3); \\ Michel Marcus, Feb 08 2016

Extensions

More terms from Michel Marcus, Feb 08 2016