%N A diagonal of the triangle A128084 of coefficients of q in the q-analog of the even double factorials: a(n) = A128084(n,n).
%C See A128082 for a diagonal of the triangle A128080 of coefficients of q in the q-analog of the odd double factorials.
%e a(n) is the n-th term in the q-analog of even double factorial (2n)!!, in which the coefficients of q (triangle A128084) begin:
%e The terms enclosed in parenthesis are initial terms of this sequence.
%o (PARI) a(n)=if(n==0,1,polcoeff(prod(k=1,n,(1-q^(2*k))/(1-q)),n,q))
%Y Cf. A000165 ((2n)!!); A128084 (triangle), A128085 (central terms).
%A _Paul D. Hanna_, Feb 14 2007