OFFSET
1,1
COMMENTS
If p>3 is a prime then 3p is in this sequence if and only if p is in A001122.
PROG
(PARI) a006694(n)=sumdiv(2*n+1, d, eulerphi(d)/znorder(Mod(2, d))) - 1;
isok(n) = (n % 2) && (a006694((n-1)/2)== 4); \\ Michel Marcus, Dec 18 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jun 16 2008
EXTENSIONS
More terms from Michel Marcus, Dec 18 2018
STATUS
approved