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Pseudoprimes to base 57.
1

%I #16 Aug 03 2014 14:01:11

%S 4,8,14,25,28,56,65,125,145,203,217,325,377,451,721,725,781,1001,1105,

%T 1625,1885,1891,2047,2296,2465,2701,2821,2911,3193,3277,3565,3625,

%U 3976,4141,4187,5365,5425,6461,6533,6601,7501,7613,8029,8401,9373,9425,10325

%N Pseudoprimes to base 57.

%C Composite numbers n such that 57^(n-1) == 1 (mod n).

%H T. D. Noe, <a href="/A020185/b020185.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 = 57; 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 *)

%o (PARI) isA020185(n) = (Mod(57,n)^(n-1)==1) && (!isprime(n))

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

%K nonn

%O 1,1

%A _David W. Wilson_