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

Terms

a(0) =0a(1) =3a(2) =11a(3) =31a(4) =79a(5) =191a(6) =447a(7) =1023a(8) =2303a(9) =5119a(10) =11263a(11) =24575a(12) =53247a(13) =114687a(14) =245759a(15) =524287a(16) =1114111a(17) =2359295a(18) =4980735a(19) =10485759a(20) =22020095a(21) =46137343a(22) =96468991a(23) =201326591a(24) =419430399a(25) =872415231a(26) =1811939327a(27) =3758096383a(28) =7784628223a(29) =16106127359