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

1,1

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

Mathematica

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

Prog

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

Crossrefs

Row 3 of A354940 (conjectured).

Intersection of A016777 and A246655.

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

Cf. also A327752, A327753.

Sequence in context: A191201 A084089 A202822 * A045090 A213382 A258867

Adjacent sequences: A137824 A137825 A137826 * A137828 A137829 A137830

Keyword

nonn,easy

Author

Eric W. Weisstein, Feb 12 2008

Status

approved