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 A085999 #11 Feb 16 2025 08:32:50
%S A085999 561,645,1729,341,1105,561,1387,2047,2465,341,2701,6601,645,4371,8321,
%T A085999 13747,29341,8911,19951,1387,30889,88561,2047,18721,60701,31621,
%U A085999 680627,4033,3277,1905,357761,74665,1419607,88357,4681,8321,422659,83333
%N A085999 For p = prime(n), a(n) is the smallest base-2 pseudoprime N (that is, 2^(N-1) = 1 mod N) such that p divides N.
%C A085999 Tables compiled by Pinch were used. Sequence A086000 lists a(n) / prime(n).
%H A085999 Amiram Eldar, <a href="/A085999/b085999.txt">Table of n, a(n) for n = 2..10001</a>
%H A085999 R. G. E. Pinch, <a href="ftp://ftp.dpmms.cam.ac.uk/pub/PSP/">Pseudoprimes and their factors (FTP)</a>.
%H A085999 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Pseudoprime.html">Pseudoprime</a>.
%e A085999 a(11) = 341 because prime(11) = 31 and 341 is the first pseudoprime divisible by 31.
%t A085999 Table[p=Prime[n]; m=MultiplicativeOrder[4, p]; k=1; While[psp=p(1+2*m*k); PowerMod[2, psp-1, psp]!=1, k++ ]; psp, {n, 2, 100}]
%Y A085999 Cf. A001567 (base-2 pseudoprimes), A086000.
%K A085999 easy,nonn
%O A085999 2,1
%A A085999 _T. D. Noe_, Jul 08 2003