OFFSET
1,2
COMMENTS
Numbers k such that 6*k+1 is a prime or the square of a prime congruent to 5 modulo 6.
If p is an Eisenstein prime of norm 6*a(n)+1 (there are two up to association if a(n) is a prime, one if a(n) is the square of a prime), then for any Eisenstein integer x, we have x^a(n) == 0, 1, w, w^2, -1, -w or -w^2 (mod p), where w = (1+sqrt(-3))/2 is a primitive sixth root of unity.
LINKS
Jianing Song, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = (A055664(n+2) - 1)/6.
EXAMPLE
4 is a term since 6*4+1 is the norm of the Eisenstein prime 5.
PROG
(PARI) isA364869(n) = isA055664(6*n+1) \\ See A055664 for its program
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Aug 11 2023
STATUS
approved