a(n) = 72*2^n -56 (n>=1).

Terms

a(0) =88a(1) =232a(2) =520a(3) =1096a(4) =2248a(5) =4552a(6) =9160a(7) =18376a(8) =36808a(9) =73672a(10) =147400a(11) =294856a(12) =589768a(13) =1179592a(14) =2359240a(15) =4718536a(16) =9437128a(17) =18874312a(18) =37748680a(19) =75497416a(20) =150994888a(21) =301989832a(22) =603979720a(23) =1207959496a(24) =2415919048a(25) =4831838152a(26) =9663676360a(27) =19327352776a(28) =38654705608a(29) =77309411272