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Pseudoprimes to base 18.
1

%I #19 Jun 13 2018 03:43:27

%S 25,49,65,85,133,221,323,325,343,425,451,637,931,1105,1225,1369,1387,

%T 1649,1729,1921,2149,2465,2701,2821,2825,2977,3325,4165,4577,4753,

%U 5525,5725,5833,5941,6305,6517,6601,7345,8911,9061,10349,10585,10961,11221

%N Pseudoprimes to base 18.

%C Composite numbers n such that 18^(n-1) == 1 (mod n). - _Michel Lagneau_, Feb 18 2012

%H T. D. Noe, <a href="/A020146/b020146.txt">Table of n, a(n) for n = 1..1000</a>

%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>

%t base = 18; t = {}; n = 1; While[Length[t] < 100, n++; If[! PrimeQ[n] && PowerMod[base, n-1, n] == 1, AppendTo[t, n]]]; t (* _T. D. Noe_, Feb 21 2012 *)

%Y Cf. A001567 (pseudoprimes to base 2).

%K nonn

%O 1,1

%A _David W. Wilson_