Number of points in Z^n of norm <= 2.

Terms

a(0) =1a(1) =5a(2) =13a(3) =33a(4) =89a(5) =221a(6) =485a(7) =953a(8) =1713a(9) =2869a(10) =4541a(11) =6865a(12) =9993a(13) =14093a(14) =19349a(15) =25961a(16) =34145a(17) =44133a(18) =56173a(19) =70529a(20) =87481a(21) =107325a(22) =130373a(23) =156953a(24) =187409a(25) =222101a(26) =261405a(27) =305713a(28) =355433a(29) =410989