a(n) = Sum_{i=0..2n} (-1)^i * T(i,2n-i), array T as in A049747.

Terms

a(0) =0a(1) =3a(2) =9a(3) =19a(4) =33a(5) =53a(6) =59a(7) =101a(8) =109a(9) =141a(10) =211a(11) =235a(12) =275a(13) =315a(14) =353a(15) =435a(16) =511a(17) =543a(18) =609a(19) =663a(20) =749a(21) =857a(22) =919a(23) =1025a(24) =1081a(25) =1211a(26) =1281a(27) =1379a(28) =1471a(29) =1579