a(n) = (46*n^5 + 30*n^4 + 15*n^3 - n) / 30.

Terms

a(0) =0a(1) =3a(2) =69a(3) =467a(4) =1858a(5) =5479a(6) =13327a(7) =28343a(8) =54596a(9) =97467a(10) =163833a(11) =262251a(12) =403142a(13) =598975a(14) =864451a(15) =1216687a(16) =1675400a(17) =2263091a(18) =3005229a(19) =3930435a(20) =5070666a(21) =6461399a(22) =8141815a(23) =10154983a(24) =12548044a(25) =15372395a(26) =18683873a(27) =22542939a(28) =27014862a(29) =32169903