a(n) = ceiling(binomial(n,6)/n).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =1a(7) =4a(8) =10a(9) =21a(10) =42a(11) =77a(12) =132a(13) =215a(14) =334a(15) =501a(16) =728a(17) =1032a(18) =1428a(19) =1938a(20) =2584a(21) =3392a(22) =4389a(23) =5609a(24) =7084a(25) =8855a(26) =10964a(27) =13455a(28) =16380a(29) =19793