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 A083735 #21 Jun 29 2019 08:32:53 %S A083735 703,1105,2465,10585,18721,19345,29341,38503,46657,50881,75361,76627, %T A083735 88831,104653,115921,146611,162401,188191,213265,226801,252601,278545, %U A083735 286903,294409,314821,334153,340561,359341,385003,385201,399001,410041 %N A083735 Pseudoprimes to bases 3 and 7. %H A083735 Amiram Eldar, <a href="/A083735/b083735.txt">Table of n, a(n) for n = 1..16479</a> (terms 1..151 from R. J. Mathar) %H A083735 F. Richman, <a href="http://math.fau.edu/Richman/carm.htm">Primality testing with Fermat's little theorem</a> %H A083735 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a> %F A083735 a(n) = n-th positive integer k(>1) such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k). %e A083735 a(1)=703 since it is the first number such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k). %t A083735 Select[Range[420000],!PrimeQ[#]&&PowerMod[3,#-1,#]==1&&PowerMod[7,#-1,#] == 1&] (* _Harvey P. Dale_, Mar 08 2014 *) %o A083735 (PARI) is(n)=!isprime(n)&&Mod(7,n)^(n-1)==1&&Mod(3,n)^(n-1)==1 \\ _Charles R Greathouse IV_, Apr 12 2012 %Y A083735 Intersection of A005935 and A005938. - _R. J. Mathar_, Apr 05 2011 %K A083735 nonn %O A083735 1,1 %A A083735 Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003