a(n) = A026626(2*n, n-2).

Terms

a(0) =1a(1) =9a(2) =40a(3) =171a(4) =703a(5) =2839a(6) =11346a(7) =45066a(8) =178330a(9) =704038a(10) =2775590a(11) =10933363a(12) =43048403a(13) =169463371a(14) =667090762a(15) =2626243774a(16) =10340952238a(17) =40727191246a(18) =160443432712a(19) =632240809054