a(n) = 2^(n-1)*(4*n-6) + 4.

Terms

a(0) =1a(1) =2a(2) =8a(3) =28a(4) =84a(5) =228a(6) =580a(7) =1412a(8) =3332a(9) =7684a(10) =17412a(11) =38916a(12) =86020a(13) =188420a(14) =409604a(15) =884740a(16) =1900548a(17) =4063236a(18) =8650756a(19) =18350084a(20) =38797316a(21) =81788932a(22) =171966468a(23) =360710148a(24) =754974724a(25) =1577058308a(26) =3288334340a(27) =6845104132a(28) =14227079172a(29) =29527900164