n*a(n) = 2*(2*n-1)*a(n-1) + 4*(n-1)*a(n-2) with a(0) = 1.

Terms

a(0) =1a(1) =2a(2) =8a(3) =32a(4) =136a(5) =592a(6) =2624a(7) =11776a(8) =53344a(9) =243392a(10) =1116928a(11) =5149696a(12) =23835904a(13) =110690816a(14) =515483648a(15) =2406449152a(16) =11258054144a(17) =52767312896a(18) =247736643584