a(n) = 7 + 12*n - 6*n^2.

Terms

a(0) =7a(1) =13a(2) =7a(3) =-11a(4) =-41a(5) =-83a(6) =-137a(7) =-203a(8) =-281a(9) =-371a(10) =-473a(11) =-587a(12) =-713a(13) =-851a(14) =-1001a(15) =-1163a(16) =-1337a(17) =-1523a(18) =-1721a(19) =-1931a(20) =-2153a(21) =-2387a(22) =-2633a(23) =-2891a(24) =-3161a(25) =-3443a(26) =-3737a(27) =-4043a(28) =-4361a(29) =-4691