a(0) = 1, a(1) = 4, a(2) = 11, and a(n) = 4*a(n-1) - 4*a(n-2) for n >= 3.

Terms

a(0) =1a(1) =4a(2) =11a(3) =28a(4) =68a(5) =160a(6) =368a(7) =832a(8) =1856a(9) =4096a(10) =8960a(11) =19456a(12) =41984a(13) =90112a(14) =192512a(15) =409600a(16) =868352a(17) =1835008a(18) =3866624a(19) =8126464a(20) =17039360a(21) =35651584a(22) =74448896a(23) =155189248a(24) =322961408a(25) =671088640a(26) =1392508928a(27) =2885681152a(28) =5972688896a(29) =12348030976