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

Terms

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