a(0) = 0; a(n) = n - a(a(a(a(n-1)))) for n > 0.

Terms

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