a(n) = 2n(19-n).

Terms

a(0) =0a(1) =36a(2) =68a(3) =96a(4) =120a(5) =140a(6) =156a(7) =168a(8) =176a(9) =180a(10) =180a(11) =176a(12) =168a(13) =156a(14) =140a(15) =120a(16) =96a(17) =68a(18) =36a(19) =0a(20) =-40a(21) =-84a(22) =-132a(23) =-184a(24) =-240a(25) =-300a(26) =-364a(27) =-432a(28) =-504a(29) =-580