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 A167028 #14 Feb 16 2015 03:48:16
%S A167028 0,1,0,6,0,120,0,5250,0,395010,0,45197460,0,7299452160,0,
%T A167028 1580682203100,0,441926274289500,0,154940341854097800,0,
%U A167028 66565404923242024800,0,34389901168124209507800,0,21034386936107260971255000,0,15032296693671903309613950000,0,12411582569784462888618434640000,0
%N A167028 Number of terms in the expansion of the determinant of a skew-symmetric matrix of order n.
%C A167028 If n is odd a(n)=0.
%C A167028 Essentially a duplicate of A002370. - _N. J. A. Sloane_, Oct 27 2009
%F A167028 Exponential generating function: (1-x^2)^(-1/4) exp(x^2/4).
%F A167028 Asymptotics (for even n): a(n)= (n!/Pi)exp( (-3log(n)+1+log(2))/4 ) GAMMA(3/4) (1+O(1/n)). [corrected by _Vaclav Kotesovec_, Feb 15 2015]. More elegant form is a(n) ~ n! * 2^(1/4) * exp(1/4) * GAMMA(3/4) / (Pi * n^(3/4)).
%e A167028 Example: the determinant of a skew symmetric matrix of order n=4 is
%e A167028 det(A)=A(1,2)A(1,2)A(3,4)A(3,4) + 2A(1,2)A(2,3)A(1,4)A(3,4) -2A(1,2)A(2,4)A(1,3)A(3,4)+ A(1,3)A(1,3)A(2,4)A(2,4)-2A(1,3)A(2,4)A(1,4)A(2,3)+A(1,4)A(1,4)A(2,3)A(2,3).
%p A167028 for n from 1 to 20 do a[n]:=n!coeftayl( (1-x^2)^(-1/4)*exp(x^2/4),x=0,n) od;
%t A167028 Rest[CoefficientList[Series[(1-x^2)^(-1/4)*E^(x^2/4), {x, 0, 20}], x] * Range[0, 20]!] (* _Vaclav Kotesovec_, Feb 15 2015 *)
%Y A167028 Cf. A002370, A167028, A002135.
%K A167028 nonn,easy
%O A167028 1,4
%A A167028 _Pietro Majer_, Oct 27 2009