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 A319383 Numbers k such that phi(k)^phi(k) == 1 (mod k^2). 0
 1, 2, 19043, 289627, 6674419, 49865347, 185014655 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS All terms are cyclic numbers (A003277). The next term, if it exists, is > 10^10. - Vaclav Kotesovec, Oct 23 2018 a(8) > 10^12, if it exists. - Giovanni Resta, Oct 25 2018 LINKS MATHEMATICA Select[Range[20000], Divisible[EulerPhi[#]^EulerPhi[#] - 1, #^2] &] (* Vaclav Kotesovec, Oct 21 2018 *) Join[{1}, Select[Range[1851*10^5], With[{c=EulerPhi[#]}, PowerMod[c, c, #^2] == 1&]]] (* Harvey P. Dale, Oct 09 2020 *) PROG (PARI) isok(n) = Mod(eulerphi(n), n^2)^eulerphi(n)==1; for(n=1, 10000000, if(isok(n), print1(n, ", "))) CROSSREFS Cf. A000010, A003277, A063439, A077816. Sequence in context: A260252 A324437 A158344 * A124364 A173156 A214598 Adjacent sequences:  A319380 A319381 A319382 * A319384 A319385 A319386 KEYWORD nonn,more AUTHOR Altug Alkan, Sep 18 2018 STATUS approved

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Last modified May 8 11:30 EDT 2021. Contains 343666 sequences. (Running on oeis4.)