a(n) = 5*2^(n+1) - 3*(n+3).

Terms

a(0) =1a(1) =8a(2) =25a(3) =62a(4) =139a(5) =296a(6) =613a(7) =1250a(8) =2527a(9) =5084a(10) =10201a(11) =20438a(12) =40915a(13) =81872a(14) =163789a(15) =327626a(16) =655303a(17) =1310660a(18) =2621377a(19) =5242814a(20) =10485691a(21) =20971448a(22) =41942965a(23) =83886002a(24) =167772079a(25) =335544236a(26) =671088553a(27) =1342177190a(28) =2684354467a(29) =5368709024