This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A243090 #16 Nov 26 2019 04:18:01 %S A243090 9,45,63,117,153,585,2169,4005,9945,13833,17865,27261,33201,36873, %T A243090 40833,57681,69345,69921,95085,140985,155961,161721,171405,186201, %U A243090 189441,192465,203841,240471,242451,244413,316881,321201,406341,481041,482769,488709,501921 %N A243090 Pseudoprimes to base 8 that are not squarefree. %C A243090 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 A243090 Intersection of A020137 and A013929. - _Michel Marcus_, Aug 21 2014 %H A243090 Amiram Eldar, <a href="/A243090/b243090.txt">Table of n, a(n) for n = 1..10000</a> %o A243090 (PARI) forcomposite(n=1, 1e9, if(Mod(8, n)^(n-1)==1, if(!issquarefree(n), print1(n, ", ")))) %Y A243090 Cf. A020137, A158358, A243010, A243089, A244065. %K A243090 nonn %O A243090 1,1 %A A243090 _Felix Fröhlich_, Aug 18 2014