a(n) = binomial(n, 2) + 6*binomial(n, 4).

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =12a(5) =40a(6) =105a(7) =231a(8) =448a(9) =792a(10) =1305a(11) =2035a(12) =3036a(13) =4368a(14) =6097a(15) =8295a(16) =11040a(17) =14416a(18) =18513a(19) =23427a(20) =29260a(21) =36120a(22) =44121a(23) =53383a(24) =64032a(25) =76200a(26) =90025a(27) =105651a(28) =123228a(29) =142912