a(n) = 1296*n^2 - 36.

Terms

a(0) =1260a(1) =5148a(2) =11628a(3) =20700a(4) =32364a(5) =46620a(6) =63468a(7) =82908a(8) =104940a(9) =129564a(10) =156780a(11) =186588a(12) =218988a(13) =253980a(14) =291564a(15) =331740a(16) =374508a(17) =419868a(18) =467820a(19) =518364a(20) =571500a(21) =627228a(22) =685548a(23) =746460a(24) =809964a(25) =876060a(26) =944748a(27) =1016028a(28) =1089900a(29) =1166364