a(0) = 1; for n >= 1, a(n) = 4*a(n-1) - (2^n - 1).

Terms

a(0) =1a(1) =3a(2) =9a(3) =29a(4) =101a(5) =373a(6) =1429a(7) =5589a(8) =22101a(9) =87893a(10) =350549a(11) =1400149a(12) =5596501a(13) =22377813a(14) =89494869a(15) =357946709a(16) =1431721301a(17) =5726754133a(18) =22906754389a(19) =91626493269a(20) =366504924501