a(n) = 4*n^3 - 3*n^2 - 2*n - 1.

Terms

a(0) =-1a(1) =-2a(2) =15a(3) =74a(4) =199a(5) =414a(6) =743a(7) =1210a(8) =1839a(9) =2654a(10) =3679a(11) =4938a(12) =6455a(13) =8254a(14) =10359a(15) =12794a(16) =15583a(17) =18750a(18) =22319a(19) =26314a(20) =30759a(21) =35678a(22) =41095a(23) =47034a(24) =53519a(25) =60574a(26) =68223a(27) =76490a(28) =85399a(29) =94974