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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =1a(8) =4a(9) =14a(10) =35a(11) =77a(12) =154a(13) =286a(14) =500a(15) =834a(16) =1334a(17) =2062a(18) =3094a(19) =4522a(20) =6460a(21) =9044a(22) =12435a(23) =16824a(24) =22432a(25) =29516a(26) =38371a(27) =49335a(28) =62790a(29) =79170