Diagonal T(n,n-2) of triangle in A071951.

Terms

a(0) =4a(1) =52a(2) =292a(3) =1092a(4) =3192a(5) =7896a(6) =17304a(7) =34584a(8) =64284a(9) =112684a(10) =188188a(11) =301756a(12) =467376a(13) =702576a(14) =1028976a(15) =1472880a(16) =2065908a(17) =2845668a(18) =3856468a(19) =5150068a(20) =6786472a(21) =8834760a(22) =11373960a(23) =14493960a(24) =18296460a(25) =22895964a(26) =28420812a(27) =35014252