a(n) = C(n-2,2)+C(n-5,5)+...+C(n-(3*floor((n-3)/3)+2),3*floor((n-3)/3)+2).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =3a(6) =6a(7) =10a(8) =15a(9) =21a(10) =29a(11) =42a(12) =66a(13) =111a(14) =192a(15) =330a(16) =554a(17) =906a(18) =1452a(19) =2303a(20) =3651a(21) =5826a(22) =9382a(23) =15225a(24) =24807a(25) =40431a(26) =65748a(27) =106584a(28) =172321a(29) =278184