a(n) = 5*(n+1)*(9*n+4).

Terms

a(0) =20a(1) =130a(2) =330a(3) =620a(4) =1000a(5) =1470a(6) =2030a(7) =2680a(8) =3420a(9) =4250a(10) =5170a(11) =6180a(12) =7280a(13) =8470a(14) =9750a(15) =11120a(16) =12580a(17) =14130a(18) =15770a(19) =17500a(20) =19320a(21) =21230a(22) =23230a(23) =25320a(24) =27500a(25) =29770a(26) =32130a(27) =34580a(28) =37120a(29) =39750