a(n) = 3*(2^(n+1)-2)*(2^(n+1)-1) + 1.

Terms

a(0) =1a(1) =19a(2) =127a(3) =631a(4) =2791a(5) =11719a(6) =48007a(7) =194311a(8) =781831a(9) =3136519a(10) =12564487a(11) =50294791a(12) =201252871a(13) =805158919a(14) =3220930567a(15) =12884312071a(16) =51538427911a(17) =206156070919a(18) =824629002247