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Bases b for which exactly one Wieferich prime p with p < b exists such that p is a base-b Wieferich prime.
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%I #9 Oct 14 2019 01:18:52

%S 5,7,8,9,10,13,21,22,23,24,25,27,29,30,31,32,33,35,38,42,43,44,45,46,

%T 48,50,54,55,60,61,64,70,74,77,78,79,85,91,94,98,100,105,110,112,113,

%U 115,120,122,126,128,131,132,133,136,138,141,150,151,152,153,154

%N Bases b for which exactly one Wieferich prime p with p < b exists such that p is a base-b Wieferich prime.

%C Numbers b such that A255920(n) = 1.

%H Felix Fröhlich, <a href="/A255922/b255922.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) is(n) = my(i=0); forprime(p=1, n-1, if(Mod(n, p^2)^(p-1)==1, i++); if(i > 1, return(0))); i==1

%Y Cf. A255920.

%Y Cf. bases b with exactly k base-b Wieferich primes less than b: A255921 (k=0), A255923 (k=2), A255924 (k=3), A255925 (k=4), A325881 (k=5), A325882 (k=6), A325883 (k=7), A325884 (k=8), A325885 (k=9), A325886 (k=10).

%K nonn

%O 1,1

%A _Felix Fröhlich_, Mar 12 2015