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

Terms

a(0) =0a(1) =3a(2) =20a(3) =70a(4) =180a(5) =385a(6) =728a(7) =1260a(8) =2040a(9) =3135a(10) =4620a(11) =6578a(12) =9100a(13) =12285a(14) =16240a(15) =21080a(16) =26928a(17) =33915a(18) =42180a(19) =51870a(20) =63140a(21) =76153a(22) =91080a(23) =108100a(24) =127400a(25) =149175a(26) =173628a(27) =200970a(28) =231420a(29) =265205