a(n) = 5*2^n - 4*n - 5.

Terms

a(0) =1a(1) =7a(2) =23a(3) =59a(4) =135a(5) =291a(6) =607a(7) =1243a(8) =2519a(9) =5075a(10) =10191a(11) =20427a(12) =40903a(13) =81859a(14) =163775a(15) =327611a(16) =655287a(17) =1310643a(18) =2621359a(19) =5242795a(20) =10485671a(21) =20971427a(22) =41942943a(23) =83885979a(24) =167772055a(25) =335544211a(26) =671088527a(27) =1342177163a(28) =2684354439