Sum of 2^n, ..., 2^(n+1) - 1.

Terms

a(0) =1a(1) =5a(2) =22a(3) =92a(4) =376a(5) =1520a(6) =6112a(7) =24512a(8) =98176a(9) =392960a(10) =1572352a(11) =6290432a(12) =25163776a(13) =100659200a(14) =402644992a(15) =1610596352a(16) =6442418176a(17) =25769738240a(18) =103079084032a(19) =412316598272