The nim-square of n.

Terms

a(0) =0a(1) =1a(2) =3a(3) =2a(4) =6a(5) =7a(6) =5a(7) =4a(8) =13a(9) =12a(10) =14a(11) =15a(12) =11a(13) =10a(14) =8a(15) =9a(16) =24a(17) =25a(18) =27a(19) =26a(20) =30a(21) =31a(22) =29a(23) =28a(24) =21a(25) =20a(26) =22a(27) =23a(28) =19a(29) =18