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%I #15 Oct 26 2018 17:25:33
%S 6,9,18,21,27,54,63,91,153,189,357,369,553,697,801,1027,1266,1387,
%T 1513,1729,1869,2701,2821,3213,3649,4033,4431,6273,6533,6541,6601,
%U 6643,7189,7957,8911,9773,9937,10649,10761,13333,13617,13833,14981,15457,15841
%N Pseudoprimes to base 55.
%C Composite numbers n such that 55^(n-1) == 1 (mod n).
%H T. D. Noe, <a href="/A020183/b020183.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 = 55; 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 *)
%t Select[Range[16000],CompositeQ[#]&&PowerMod[55,#-1,#]==1&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 26 2018 *)
%Y Cf. A001567 (pseudoprimes to base 2).
%K nonn
%O 1,1
%A _David W. Wilson_
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