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

Terms

a(0) =0a(1) =1a(2) =7a(3) =33a(4) =139a(5) =565a(6) =2271a(7) =9097a(8) =36403a(9) =145629a(10) =582535a(11) =2330161a(12) =9320667a(13) =37282693a(14) =149130799a(15) =596523225a(16) =2386092931a(17) =9544371757a(18) =38177487063a(19) =152709948289a(20) =610839793195