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 A246006 #70 Apr 15 2023 15:43:01
%S A246006 1,1,1,1,1,5,1,61,1,1385,5,50521,691,2702765,7,199360981,3617,
%T A246006 19391512145,43867,2404879675441,174611,370371188237525,854513,
%U A246006 69348874393137901,236364091,15514534163557086905,8553103,4087072509293123892361,23749461029,1252259641403629865468285
%N A246006 a(2n) = numerator of |Bernoulli(2n)|, a(2n+1) = Euler(2n).
%C A246006 Primes p which divide at least one a(n) for n<=p-2 are called weakly-irregular primes. For example, 19|a(11), 31|a(23), 37|a(32), 43|a(13), 47|a(15), 59|a(44), 61|a(7), ... - _Eric Chen_, Nov 26 2014
%C A246006 The weakly-irregular primes below 500 are 19, 31, 37, 43, 47, 59, 61, 67, 71, 79, 101, 103, 131, 137, 139, 149, 157, 193, 223, 233, 241, 251, 257, 263, 271, 277, 283, 293, 307, 311, 347, 349, 353, 359, 373, 379, 389, 401, 409, 419, 421, 433, 461, 463, 467, 491. - _Eric Chen_, Nov 26 2014
%C A246006 A prime can divide more than one a(n) for n<=p-2; for example, 67 divides both a(27) and a(58); additional examples are 101, 149, 157, 241, 263, 307, 311, ... . - _Eric Chen_, Nov 26 2014
%C A246006 Smallest values of k such that the n-th weakly-irregular prime divides a(k) are 11, 23, 32, 13, 15, 44, 7, 27, 29, 19, 63, 24, 22, 43, 129, 130, 62, 75, ... . - _Eric Chen_, Nov 26 2014
%C A246006 Smallest prime factors (>= n+2) of a(n) are 1, 1, 1, 1, 1, 1, 1, 61, 1, 277, 1, 19, 691, 43, 1, 47, 3617, 228135437, 43867, 79, 283, 41737, 131, 31, 103, 2137, 657931, 67, 9349, 71, ... . - _Eric Chen_, Nov 26 2014
%C A246006 The irregular pairs are (61, 7), (277, 9), (19, 11), (2659, 11), (691, 12), (43, 13), (967, 13), (47, 15), (4241723, 15), (3617, 16), (228135437, 17), (43867, 18), (79, 19), (349, 19), (84224971, 19), ... . - _Eric Chen_, Nov 26 2014
%H A246006 Eric Chen, <a href="/A246006/b246006.txt">Table of n, a(n) for n = 0..199</a>
%H A246006 Peter Luschny, <a href="http://www.luschny.de/math/primes/irregular.html"> Irregular primes</a>
%H A246006 Wikipedia, <a href="http://en.wikipedia.org/wiki/Irregular_prime"> Irregular prime</a>
%e A246006 Euler(10) = 50521, so a(11) = 50521.
%e A246006 Bernoulli(12) = 691/2730, so a(12) = 691.
%t A246006 a246006[n_] := If[EvenQ[n], Abs[Numerator[BernoulliB[n]]], Abs[EulerE[n-1]]]; Table[a246006[n], {n, 0, 99}]
%o A246006 (Python)
%o A246006 from sympy import euler, bernoulli
%o A246006 def A246006(n): return abs(euler(n-1)) if n&1 else abs(bernoulli(n)).p # _Chai Wah Wu_, Apr 15 2023
%Y A246006 Cf. A027641, A122045, A000367, A028296, A000111, A000364, A000182.
%Y A246006 Cf. A050970, A050971, A068205.
%K A246006 nonn
%O A246006 0,6
%A A246006 _Eric Chen_, Nov 13 2014