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 A380978 #25 Mar 18 2025 22:21:44
%S A380978 2,3,5,7,13,11,17,41,37,19,31,43,23,53,29,101,61,109,71,67,73,113,151,
%T A380978 89,97,211,191,157,163,193,139,281,107,103,181,47,127,271,131,307,59,
%U A380978 257,229,331,337,199,241,461,239,617,367,263,401,251,149,421,137,277
%N A380978 Sequence of minimal Fermat witnesses for compositeness. a(n) is the least k such that the smallest composite number that is a Fermat pseudoprime to bases {a(i) : 1 <= i < n} is not a Fermat pseudoprime to base k.
%H A380978 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FermatPseudoprime.html">Fermat Pseudoprime</a>, <a href="https://mathworld.wolfram.com/Witness.html">Witness</a>
%H A380978 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>
%F A380978 a(1) = 2, otherwise a(n) = A321790(k), where k is such that A001567(k) = A380979(n). - _Peter Munn_, Mar 12 2025
%e A380978 For n = 1, a(1) = 2, since 2 is the first Fermat witness, proving the compositeness of 4.
%e A380978 For n = 2, a(2) = 3, since 3 is the next required Fermat witness, proving the compositeness of 341 (all previous composites are witnessed by 2).
%e A380978 For n = 3, a(3) = 5, since 5 is the next required Fermat witness, proving the compositeness of 1105 (all previous composites are witnessed by 2 and 3).
%Y A380978 Cf. A001567, A089105, A321790, A380979.
%K A380978 nonn
%O A380978 1,1
%A A380978 _Jan Kostanjevec_, Feb 10 2025
%E A380978 More terms from _Jinyuan Wang_, Mar 05 2025