Sum of binary numbers with n 1's and one (possibly leading) 0.

Terms

a(0) =0a(1) =3a(2) =14a(3) =45a(4) =124a(5) =315a(6) =762a(7) =1785a(8) =4088a(9) =9207a(10) =20470a(11) =45045a(12) =98292a(13) =212979a(14) =458738a(15) =983025a(16) =2097136a(17) =4456431a(18) =9437166a(19) =19922925a(20) =41943020a(21) =88080363a(22) =184549354a(23) =385875945a(24) =805306344a(25) =1677721575a(26) =3489660902a(27) =7247757285a(28) =15032385508