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 A084653 #8 Feb 16 2025 08:32:49 %S A084653 341,1387,2047,8321,13747,18721,19951,31621,60701,83333,88357,219781, %T A084653 275887,422659,435671,513629,514447,587861,604117,653333,680627, %U A084653 710533,722261,741751,769757,916327,1194649,1252697,1293337,1433407,1441091 %N A084653 Pseudoprimes whose prime factors do not divide any smaller pseudoprime. %C A084653 Here pseudoprime means a Fermat base-2 pseudoprime; sequence A001567, a composite number n such that n divides 2^(n-1) - 1. All numbers in this sequence seem to have only two prime factors - a conjecture that has been tested for all pseudoprimes < 10^15. The two prime factors are given in A084654 and A084655. The two prime factors are the same when the pseudoprime is the square of a Wieferich prime (A001220). %H A084653 T. D. Noe, <a href="/A084653/b084653.txt">Table of n, a(n) for n = 1..10000</a> %H A084653 R. G. E. Pinch, <a href="ftp://ftp.dpmms.cam.ac.uk/pub/PSP/">Pseudoprimes and their factors (FTP)</a> %H A084653 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Pseudoprime.html">Pseudoprime</a> %H A084653 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a> %e A084653 a(2) = 1387 because 1387 = 19*73 and the smaller pseudoprimes (341, 561, 645, 1105) do not have the factors 19 or 73. %Y A084653 Cf. A001220, A001567, A084654, A084655. %K A084653 nonn %O A084653 1,1 %A A084653 _T. D. Noe_, Jun 02 2003