a(n) = 2^(n-1)*(8*n-14) + 8.

Terms

a(0) =1a(1) =2a(2) =12a(3) =48a(4) =152a(5) =424a(6) =1096a(7) =2696a(8) =6408a(9) =14856a(10) =33800a(11) =75784a(12) =167944a(13) =368648a(14) =802824a(15) =1736712a(16) =3735560a(17) =7995400a(18) =17039368a(19) =36175880a(20) =76546056a(21) =161480712a(22) =339738632a(23) =713031688a(24) =1493172232a(25) =3120562184a(26) =6509559816a(27) =13555990536a(28) =28185722888a(29) =58518929416