A137827 Prime powers (A246655) congruent to 1 (mod 3).

4, 7, 13, 16, 19, 25, 31, 37, 43, 49, 61, 64, 67, 73, 79, 97, 103, 109, 121, 127, 139, 151, 157, 163, 169, 181, 193, 199, 211, 223, 229, 241, 256, 271, 277, 283, 289, 307, 313, 331, 337, 343, 349, 361, 367, 373, 379, 397, 409, 421, 433, 439, 457, 463, 487, 499

Offset: 1

Author

Eric W. Weisstein, Feb 12 2008

Keywords

• nonn
• easy

Comments

Numbers k not being powers of 3 such that x^2 + x + 1 (or x^2 - x + 1) is reducible over GF(k). - Jianing Song, Sep 24 2019

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Cyclotomic Graph

Crossrefs

Row 3 of A354940 (conjectured).

Intersection of A016777 and A246655.

Cf. A354982 (characteristic function), A354984 (terms * 3).

Cf. also A327752, A327753.

Programs

Mathematica

Select[ Range[4, 500], (Mod[#, 3] == 1 && Mod[#, # - EulerPhi[#]] == 0)& ] (* Jean-François Alcover, Oct 26 2012 *)

PARI

isok(n) = isprimepower(n) && ((n % 3) == 1); \\ Michel Marcus, Sep 24 2019