4-wave sequence.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =4a(7) =7a(8) =9a(9) =10a(10) =19a(11) =26a(12) =30a(13) =56a(14) =75a(15) =85a(16) =160a(17) =216a(18) =246a(19) =462a(20) =622a(21) =707a(22) =1329a(23) =1791a(24) =2037a(25) =3828a(26) =5157a(27) =5864a(28) =11021a(29) =14849