a(n) = n*(5*n - 1)/2.

Terms

a(0) =0a(1) =2a(2) =9a(3) =21a(4) =38a(5) =60a(6) =87a(7) =119a(8) =156a(9) =198a(10) =245a(11) =297a(12) =354a(13) =416a(14) =483a(15) =555a(16) =632a(17) =714a(18) =801a(19) =893a(20) =990a(21) =1092a(22) =1199a(23) =1311a(24) =1428a(25) =1550a(26) =1677a(27) =1809a(28) =1946a(29) =2088