a(0) = 121; for n>0, a(n) = a(n-1) - n + 1.

Terms

a(0) =121a(1) =121a(2) =120a(3) =118a(4) =115a(5) =111a(6) =106a(7) =100a(8) =93a(9) =85a(10) =76a(11) =66a(12) =55a(13) =43a(14) =30a(15) =16a(16) =1a(17) =-15a(18) =-32a(19) =-50a(20) =-69a(21) =-89a(22) =-110a(23) =-132a(24) =-155a(25) =-179a(26) =-204a(27) =-230a(28) =-257a(29) =-285