Number of points in Z^n of norm <= 4.

Terms

a(0) =1a(1) =9a(2) =49a(3) =257a(4) =1281a(5) =5913a(6) =23793a(7) =88273a(8) =306049a(9) =995241a(10) =3083569a(11) =9217057a(12) =26631041a(13) =74164665a(14) =198807793a(15) =513829617a(16) =1284656385a(17) =3117323593a(18) =7360510001a(19) =16939394369a(20) =38039783425a(21) =83427144281a(22) =178841051889