OFFSET
1,1
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.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
r[n_] := EulerPhi[n]/MultiplicativeOrder[2, n]; Select[Range[5000], Total@(r /@ Divisors[#]) - 1 == 3 &] (* Amiram Eldar, Sep 12 2019 *)
PROG
(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
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jun 15 2008
EXTENSIONS
More terms from Michel Marcus, Feb 08 2016
STATUS
approved