Hofstadter H-sequence: a(n) = n - a(a(a(n-1))).

Terms

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