a(1) = a(2) = a(3) = a(4) = 1, a(n) = a(a(n-1))+a(n-a(n-1)) for n >= 5.

Terms

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