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%I #20 May 15 2022 07:30:24
%S 5,29,42,75,132,134,140,152,159,162,163,201,206,215,241,256,277,301,
%T 314,347,404,406,412,424,431,434,435,473,478,487,513,528,549,573,586,
%U 619,676,678,684,696,703,706,707,745,750,759,785,800,821,845,858,891,948
%N Numbers k such that 17 divides 3^k-k.
%C Suggested by a problem in a web page by Hojoo Lee entitled "Challenging problems in number theory". However, the page no longer exists.
%H Amiram Eldar, <a href="/A081116/b081116.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Rec#order_16">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2,-2,2,-2,2,-2,2,-2,2,-2,2,-2,2,-1).
%F a(n+1)-a(n) is the 16-periodic sequence (24, 13, 33, 57, 2, 6, 12, 7, 3, 1, 38, 5, 9, 26, 15, 21).
%t Select[Range[1000], PowerMod[3, #, 17] == Mod[#, 17] &] (* _Amiram Eldar_, May 14 2022 *)
%o (PARI) isok(n) = Mod(3, 17)^n == Mod(n, 17); \\ _Michel Marcus_, Dec 02 2013
%Y Cf. A024024 (3^n-n).
%K nonn
%O 1,1
%A _Benoit Cloitre_, Apr 16 2003