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 A194590 #13 Jun 26 2019 07:54:04
%S A194590 0,0,1,-2,7,-14,38,-76,187,-374,874,-1748,3958,-7916,17548,-35096,
%T A194590 76627,-153254,330818,-661636,1415650,-2831300,6015316,-12030632,
%U A194590 25413342,-50826684,106853668,-213707336,447472972,-894945944,1867450648,-3734901296,7770342787
%N A194590 a(n) = (-1)^n*(A056040(n+1)*A152271(n)-2^n)/2.
%C A194590 The binomial transform of a(n) are the complementary Riordan numbers A194589 (see link).
%H A194590 Peter Luschny, <a href="http://oeis.org/wiki/User:Peter_Luschny/TheLostCatalanNumbers">The lost Catalan numbers</a>
%F A194590 a(n) = Sum_{k=0..n} (-1)^(n-k)*binomial(n,k)*cr(k), where cr(k) are the complementary Riordan numbers A194589.
%p A194590 A056040 := n -> n!/iquo(n,2)!^2:
%p A194590 A152271 := n -> `if`(n mod 2 = 0, 1, (n+1)/2):
%p A194590 A194590 := n -> (-1)^n*(A056040(n+1)*A152271(n)-2^n)/2:
%t A194590 sf[n_] := n!/Quotient[n, 2]!^2;
%t A194590 a[n_] := (-1)^n (sf[n + 1] * If[EvenQ[n], 1, (n + 1)/2] - 2^n)/2;
%t A194590 Table[a[n], {n, 0, 32}] (* _Jean-François Alcover_, Jun 26 2019 *)
%Y A194590 Cf. A107373 (has offset 1).
%K A194590 sign
%O A194590 0,4
%A A194590 _Peter Luschny_, Aug 30 2011