a(n) = -n^2 + 9*n + 53.

Terms

a(0) =53a(1) =61a(2) =67a(3) =71a(4) =73a(5) =73a(6) =71a(7) =67a(8) =61a(9) =53a(10) =43a(11) =31a(12) =17a(13) =1a(14) =-17a(15) =-37a(16) =-59a(17) =-83a(18) =-109a(19) =-137a(20) =-167a(21) =-199a(22) =-233a(23) =-269a(24) =-307a(25) =-347a(26) =-389a(27) =-433a(28) =-479a(29) =-527