Number of points in N^n of norm <= 3.

Terms

a(0) =1a(1) =4a(2) =11a(3) =29a(4) =70a(5) =157a(6) =337a(7) =702a(8) =1420a(9) =2780a(10) =5258a(11) =9615a(12) =17043a(13) =29381a(14) =49430a(15) =81404a(16) =131563a(17) =209084a(18) =327237a(19) =504945a(20) =768820a(21) =1155781a(22) =1716375a(23) =2518938a(24) =3654750a(25) =5244356a(26) =7445244a(27) =10461091a(28) =14552809a(29) =20051645