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 A380979 #29 Mar 18 2025 22:21:57
%S A380979 4,341,1105,1729,29341,75361,162401,252601,294409,334153,399001,
%T A380979 1152271,1615681,2508013,3581761,3828001,6189121,6733693,10024561,
%U A380979 10267951,14469841,17098369,17236801,19384289,23382529,29111881,34657141,53711113,64377991,79411201,79624621
%N A380979 Composites that cause a witness to be added to a set of Fermat witnesses: a(n) is the smallest composite number that is not guaranteed composite using Fermat's Little Theorem by the witness A380978(i) for any i < n.
%C A380979 A380978(n) is defined as the minimal Fermat witness that guarantees the compositeness of a(n). See the Weisstein link for details of the guarantee -- the option that uses a property derived from Fermat's little theorem.
%C A380979 To what extent does this differ from A135720 sorted? - _Peter Munn_, Mar 12 2025
%H A380979 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CompositenessCertificate.html">Compositeness Certificate</a>
%H A380979 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>
%e A380979 a(1) = 4, since 4 is the smallest composite number and we need to add a witness to the empty set to guarantee its compositeness. 2 is the minimal Fermat witness for the compositeness of 4, so the set of witnesses becomes {2}.
%e A380979 a(2) = 341, since 341 is the smallest composite number that requires a witness other than 2, namely 3.
%e A380979 a(3) = 1105, since 1105 is the smallest composite number that requires a witness other than 2 and 3, namely 5.
%Y A380979 Cf. A001567, A002997, A006945, A098654, A135720, A380978 (new minimal Fermat witness).
%K A380979 nonn
%O A380979 1,1
%A A380979 _Jan Kostanjevec_, Feb 10 2025
%E A380979 More terms from _Jinyuan Wang_, Mar 05 2025