%I #13 Aug 03 2014 14:01:10
%S 26,65,91,121,133,247,259,286,341,365,481,671,703,949,1001,1105,1541,
%T 1649,1729,1891,2071,2465,2665,2701,2821,2981,2993,3146,3281,3367,
%U 3605,3751,4033,4745,4921,4961,5299,5461,5551,5611,5621,6305,6533,6601,7381
%N Pseudoprimes to base 27.
%C Composite numbers n such that 27^(n-1) == 1 (mod n).
%H T. D. Noe, <a href="/A020155/b020155.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 = 27; 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_