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 A308646 #11 Feb 16 2025 08:33:55
%S A308646 1,0,1,-9,50,413,-17731,110176,9938669,-278475061,-9816860358,
%T A308646 725503033401,15823587507881,-2848115497132448,-38795579403211671,
%U A308646 17235101634895315375,153440975825762815938,-156894403296377741177371,-1454252568471818731501051,2071137586315785548669378432
%N A308646 a(n) = exp(1) * Sum_{k>=0} (-1)^k*k^(2*n)/k!.
%H A308646 Robert Israel, <a href="/A308646/b308646.txt">Table of n, a(n) for n = 0..297</a>
%H A308646 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ComplementaryBellNumber.html">Complementary Bell Number</a>
%F A308646 a(n) = Sum_{k=0..2*n} (-1)^k*Stirling2(2*n,k).
%F A308646 a(n) = A000587(2*n).
%p A308646 seq(BellB(2*n,-1),n=0..30); # _Robert Israel_, Jun 08 2020
%t A308646 Table[Exp[1] Sum[(-1)^k k^(2 n)/k!, {k, 0, Infinity}], {n, 0, 19}]
%t A308646 Table[BellB[2 n, -1], {n, 0, 19}]
%Y A308646 Cf. A000587, A020557, A308647.
%K A308646 sign
%O A308646 0,4
%A A308646 _Ilya Gutkovskiy_, Jun 13 2019