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 A020209 Pseudoprimes to base 81. 1

%I

%S 4,8,10,16,20,28,40,52,70,80,85,91,112,121,130,176,190,205,208,232,

%T 280,286,292,364,370,451,496,511,520,532,616,671,697,703,730,742,910,

%U 946,949,965,976,1036,1105,1168,1261,1288,1387,1435,1456,1541,1606,1729,1891

%N Pseudoprimes to base 81.

%C Composite numbers n such that 81^(n-1) == 1 (mod n).

%H T. D. Noe, <a href="/A020209/b020209.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 = 81; 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_

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