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 A083733 #19 Jun 29 2019 08:33:52 %S A083733 561,1105,2465,3277,8321,10585,18721,29341,46657,62745,75361,104653, %T A083733 115921,162401,219781,226801,252601,278545,294409,314821,334153, %U A083733 340561,399001,410041,449065,488881,512461,530881,534061,552721,574561,587861 %N A083733 Pseudoprimes to bases 2 and 7. %H A083733 Amiram Eldar, <a href="/A083733/b083733.txt">Table of n, a(n) for n = 1..15498</a> (terms 1..138 from R. J. Mathar) %H A083733 F. Richman, <a href="http://math.fau.edu/Richman/carm.htm">Primality testing with Fermat's little theorem</a> %H A083733 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a> %F A083733 a(n) = n-th positive integer k(>1) such that 2^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k). %e A083733 a(1)=561 since it is the first positive integer k(>1) which satisfies 2^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k). %o A083733 (PARI) is(n)=!isprime(n)&&Mod(2,n)^(n-1)==1&&Mod(7,n)^(n-1)==1 \\ _Charles R Greathouse IV_, Apr 12 2012 %Y A083733 Intersection of A005938 and A001567. - _R. J. Mathar_, Apr 05 2011 %K A083733 nonn %O A083733 1,1 %A A083733 Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003