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Pseudoprimes to base 8 that are not squarefree.
5

%I #16 Nov 26 2019 04:18:01

%S 9,45,63,117,153,585,2169,4005,9945,13833,17865,27261,33201,36873,

%T 40833,57681,69345,69921,95085,140985,155961,161721,171405,186201,

%U 189441,192465,203841,240471,242451,244413,316881,321201,406341,481041,482769,488709,501921

%N Pseudoprimes to base 8 that are not squarefree.

%C Any member of the sequence is divisible by the square of a base 8 Wieferich prime, of which only three cases are known, namely 3, 1093 and 3511.

%C Intersection of A020137 and A013929. - _Michel Marcus_, Aug 21 2014

%H Amiram Eldar, <a href="/A243090/b243090.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) forcomposite(n=1, 1e9, if(Mod(8, n)^(n-1)==1, if(!issquarefree(n), print1(n, ", "))))

%Y Cf. A020137, A158358, A243010, A243089, A244065.

%K nonn

%O 1,1

%A _Felix Fröhlich_, Aug 18 2014