OFFSET
1,1
COMMENTS
Equivalently, primes p not congruent to 1 (mod 8).
In 1981 D. Weisser proved that a prime not congruent to 1 (mod 8) and >= 7 is irregular if and only if the rational number Zeta_K(-1) is p-adically integral, that is has a denominator not divisible by p, where K is the maximal real subfield of the cyclotomic field of p-th roots of unity. - From Achava Nakhash posting, see Links.
LINKS
Ray Chandler, Table of n, a(n) for n = 1..10000 (first 1000 terms from Vincenzo Librandi)
Achava Nakhash, Irregular Primes and Dedekind Zeta Functions
MATHEMATICA
Select[Prime[Range[100]], MemberQ[{2, 3, 5, 7}, Mod[#, 8]]&] (* Harvey P. Dale, Mar 24 2011 *)
PROG
(Magma) [p: p in PrimesUpTo(1200) | p mod 8 in [2, 3, 5, 7]]; // Vincenzo Librandi, Aug 08 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved