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

Terms

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