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 A137827 Prime powers (A246655) congruent to 1 (mod 3). 2
 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 (list; graph; refs; listen; history; text; internal format)
 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 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 Intersection of A016777 and A246655. 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

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Last modified June 24 18:46 EDT 2021. Contains 345419 sequences. (Running on oeis4.)