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 A325659 #26 Jun 09 2019 15:09:22
%S A325659 15,40,21,156,259,57,585,91,111,133,1885,183,2955,3616,273,5220,343,
%T A325659 381,8421,9724,507,553,14425,651,703,20440,813,871,931,993,1057,37060,
%U A325659 1191,1261,1333,1407,56355,1561,1641,70644,1807,1893,1981,2071,2163,2257,2353,2451,127551
%N A325659 Smallest Brazilian composite in base n >= 2 which can be represented as a string of three or more 1's in this base.
%C A325659 Also the smallest Brazilian composite of the form (n^k - 1)/(n - 1) with k > 2.
%C A325659 For Mersenne numbers = (11...11)_2 = 2^k-1 in A000225, there is a smaller integer which is Brazilian prime: 7, so 7 is the first term of A285642 and another one is the smaller composite 15, so 15 is the first term of this sequence.
%C A325659 For numbers (11...11)_3 = (3^k-1)/2 in A003462, there is also a smaller integer which is Brazilian prime:13, so 13 is the second term of A285642 and another one is the smaller Brazilian composite: 40, so 40 is the second term of this sequence.
%C A325659 For numbers like (11...11)_4 = (4^k-1)/3, the terms are respectively 0 in A285642 because there is no Brazilian prime of this type and 21 for composite numbers of this sequence, and so on.
%H A325659 Wikipedia, <a href="https://fr.wikipedia.org/wiki/Nombre_br%C3%A9silien">Nombre brésilien</a>
%e A325659 15 = (1111)_2, 40 = (1111)_3, 21 = (111)_4, 156 = (1111)_5.
%o A325659 (PARI) a(n) = {my(k=4, x); while (isprime(x=(n^(k-1)-1)/(n-1)), k++); x;} \\ _Michel Marcus_, May 17 2019
%Y A325659 Subsequence of A053696, A220571, A325658.
%Y A325659 Cf. A285642 (same with Brazilian primes).
%K A325659 nonn,base
%O A325659 2,1
%A A325659 _Bernard Schott_, May 12 2019
%E A325659 More terms from _Michel Marcus_, May 17 2019