OFFSET
1,1
COMMENTS
For these odd primes delta(p) = A055034(n) = (p-1)/2 is squarefree, and therefore the (Abelian) multiplicative group Modd p (see a comment on A203571 for Modd n, not to be confused with mod n) is guaranteed to be cyclic. This is because the number of Abelian groups of order n (A000688) is 1 precisely for the squarefree numbers A005117. See also A210845. One can in fact prove that the multiplicative group Modd p is cyclic for all primes (the case p=2 is trivial). - Wolfdieter Lang, Sep 24 2012
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[2 * Select[Range[200], SquareFreeQ] + 1, PrimeQ] (* Amiram Eldar, Feb 22 2021 *)
PROG
(PARI) isok(p) = isprime(p) && (p>2) && issquarefree((p-1)/2); \\ Michel Marcus, Feb 22 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 10 2002
STATUS
approved