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Pseudoprimes to base 78.
1

%I #20 Oct 11 2019 11:02:11

%S 77,341,385,451,553,703,869,1045,1247,1271,1441,1849,1921,2047,2465,

%T 2765,3097,4061,4187,4345,4577,5371,6031,6083,6085,6545,6601,8321,

%U 8911,8965,10585,13333,13981,15211,15251,15841,17711,17767,20689,22801,23281,23617

%N Pseudoprimes to base 78.

%C Composite numbers n such that 78^(n-1) == 1 (mod n). - _Michel Lagneau_, Feb 18 2012

%H T. D. Noe, <a href="/A020206/b020206.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 = 78; 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[25000],CompositeQ[#]&&PowerMod[78,#-1,#]==1&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 11 2019 *)

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

%K nonn

%O 1,1

%A _David W. Wilson_