Write n in binary, interchange 0's and 1's, convert back to decimal.

Terms

a(0) =1a(1) =0a(2) =1a(3) =0a(4) =3a(5) =2a(6) =1a(7) =0a(8) =7a(9) =6a(10) =5a(11) =4a(12) =3a(13) =2a(14) =1a(15) =0a(16) =15a(17) =14a(18) =13a(19) =12a(20) =11a(21) =10a(22) =9a(23) =8a(24) =7a(25) =6a(26) =5a(27) =4a(28) =3a(29) =2