a(n) = 20*binomial(n,6) + 2*binomial(n,3) + 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =9a(5) =21a(6) =61a(7) =211a(8) =673a(9) =1849a(10) =4441a(11) =9571a(12) =18921a(13) =34893a(14) =60789a(15) =101011a(16) =161281a(17) =248881a(18) =372913a(19) =544579a(20) =777481a(21) =1087941a(22) =1495341a(23) =2022483a(24) =2695969a(25) =3546601a(26) =4609801a(27) =5926051a(28) =7541353a(29) =9507709