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A055687 Numbers k such that 4^k == -1 (mod k-1). 3

%I

%S 2,18,4098,7362,85074,658530,3999138,72281282,285143058,628944690,

%T 854112114,1423081170,2561019282,3111576930,4298117634,5921265042,

%U 14224884930,21336998130,34317377234,50723421714,63797137890,144269032050,163834314354,187397322210,212565453282,231286579794,232992827298,266198715090,314834584482,348160787730,580045717650,706501722498

%N Numbers k such that 4^k == -1 (mod k-1).

%t Do[If[PowerMod[4, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]

%K nonn

%O 1,1

%A _Robert G. Wilson v_, Jun 09 2000

%E Terms a(9) onward from _Max Alekseyev_, Oct 12 2012

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Last modified October 6 00:49 EDT 2022. Contains 357261 sequences. (Running on oeis4.)