a(n) = 60*2^n - 48 (n>=1).

Terms

a(0) =72a(1) =192a(2) =432a(3) =912a(4) =1872a(5) =3792a(6) =7632a(7) =15312a(8) =30672a(9) =61392a(10) =122832a(11) =245712a(12) =491472a(13) =982992a(14) =1966032a(15) =3932112a(16) =7864272a(17) =15728592a(18) =31457232a(19) =62914512a(20) =125829072a(21) =251658192a(22) =503316432a(23) =1006632912a(24) =2013265872a(25) =4026531792a(26) =8053063632a(27) =16106127312a(28) =32212254672a(29) =64424509392