a(n) = -n^2 + 9*n + 23.

Terms

a(0) =23a(1) =31a(2) =37a(3) =41a(4) =43a(5) =43a(6) =41a(7) =37a(8) =31a(9) =23a(10) =13a(11) =1a(12) =-13a(13) =-29a(14) =-47a(15) =-67a(16) =-89a(17) =-113a(18) =-139a(19) =-167a(20) =-197a(21) =-229a(22) =-263a(23) =-299a(24) =-337a(25) =-377a(26) =-419a(27) =-463a(28) =-509a(29) =-557