a(n) = 1 + 3*n - 2*n^2.

Terms

a(0) =1a(1) =2a(2) =-1a(3) =-8a(4) =-19a(5) =-34a(6) =-53a(7) =-76a(8) =-103a(9) =-134a(10) =-169a(11) =-208a(12) =-251a(13) =-298a(14) =-349a(15) =-404a(16) =-463a(17) =-526a(18) =-593a(19) =-664a(20) =-739a(21) =-818a(22) =-901a(23) =-988a(24) =-1079a(25) =-1174a(26) =-1273a(27) =-1376a(28) =-1483a(29) =-1594