Restricted combinations.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =12a(5) =18a(6) =27a(7) =45a(8) =75a(9) =125a(10) =200a(11) =320a(12) =512a(13) =832a(14) =1352a(15) =2197a(16) =3549a(17) =5733a(18) =9261a(19) =14994a(20) =24276a(21) =39304a(22) =63580a(23) =102850a(24) =166375a(25) =269225a(26) =435655a(27) =704969a(28) =1140624a(29) =1845504