a(n) = binomial(n,4) + binomial(n,2).

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =15a(5) =30a(6) =56a(7) =98a(8) =162a(9) =255a(10) =385a(11) =561a(12) =793a(13) =1092a(14) =1470a(15) =1940a(16) =2516a(17) =3213a(18) =4047a(19) =5035a(20) =6195a(21) =7546a(22) =9108a(23) =10902a(24) =12950a(25) =15275a(26) =17901a(27) =20853a(28) =24157a(29) =27840