a(n) = binomial(n+3, 4) + binomial(n+1, 3) + 1.

Terms

a(0) =1a(1) =2a(2) =7a(3) =20a(4) =46a(5) =91a(6) =162a(7) =267a(8) =415a(9) =616a(10) =881a(11) =1222a(12) =1652a(13) =2185a(14) =2836a(15) =3621a(16) =4557a(17) =5662a(18) =6955a(19) =8456a(20) =10186a(21) =12167a(22) =14422a(23) =16975a(24) =19851a(25) =23076a(26) =26677a(27) =30682a(28) =35120a(29) =40021