a(n) = n*4^n - 1, with a(0) = 1.

Terms

a(0) =1a(1) =3a(2) =31a(3) =191a(4) =1023a(5) =5119a(6) =24575a(7) =114687a(8) =524287a(9) =2359295a(10) =10485759a(11) =46137343a(12) =201326591a(13) =872415231a(14) =3758096383a(15) =16106127359a(16) =68719476735a(17) =292057776127