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 A132184 #10 Feb 16 2025 08:33:06
%S A132184 6,21,27,321,1266,1527,1821,2526,2576,2721,2950,3126,3246,3426,4206,
%T A132184 4236,4821,4926,5286,5721,5946,5950,6100,6351,7018,7138,7172,7386,
%U A132184 7806,7931,8037,8790,8796,8826,9021,9048,9426,9478,9726,9921,10221,10326
%N A132184 Numbers k such that the numerator of the Bernoulli number B(2k) ends with the digits 691.
%C A132184 The numerator of BernoulliB(12) is 691. The sequence gives semi-indices of the 691-automorphic numerators in the BernoulliB(n) sequence. All 4 initial terms are multiples of 3. Note that Bernoulli numerators corresponding to the first two terms are the automorphic primes: 691 and 1520097643918070802691.
%H A132184 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BernoulliNumber.html">Bernoulli Number</a>.
%e A132184 6 is a term because BernoulliB(2*6) = -691/2730.
%e A132184 21 is a term because BernoulliB(2*21) = 1520097643918070802691/1806.
%e A132184 27 is a term because BernoulliB(2*27) = 29149963634884862421418123812691/798.
%t A132184 Do[ g=Numerator[ BernoulliB[ 2n ] ]; f=Mod[ Abs[ g ], 1000 ]; If[ f==691, Print[ n ] ], {n,1,1000}]
%t A132184 Select[Range[10400],Mod[Abs[Numerator[BernoulliB[2#]]],1000]==691&] (* _Harvey P. Dale_, May 05 2019 *)
%Y A132184 Cf. A000367 (numerators of Bernoulli numbers B_2n).
%Y A132184 Cf. A092132 (indices k of Bernoulli numbers B(k) whose numerators are primes).
%Y A132184 Cf. A092133 (prime numerators of Bernoulli numbers).
%K A132184 base,nonn
%O A132184 1,1
%A A132184 _Alexander Adamchuk_, Nov 04 2007
%E A132184 a(5)-a(42) from _Donovan Johnson_, Sep 05 2008