190253629440domain: NAppears in sequencesa(n) is n! times the coefficient of Pi^floor(n/2) in the volume of an n-dimensional unit ball.at n=19A094941Expansion of e.g.f. (1+4*x)/(1-4*x).at n=9A098560a(n) = 2^n * floor(n/2)!at n=19A271216