a(n) = 72*n^2 - 1.

Terms

a(0) =71a(1) =287a(2) =647a(3) =1151a(4) =1799a(5) =2591a(6) =3527a(7) =4607a(8) =5831a(9) =7199a(10) =8711a(11) =10367a(12) =12167a(13) =14111a(14) =16199a(15) =18431a(16) =20807a(17) =23327a(18) =25991a(19) =28799a(20) =31751a(21) =34847a(22) =38087a(23) =41471a(24) =44999a(25) =48671a(26) =52487a(27) =56447a(28) =60551a(29) =64799