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

Terms

a(0) =1a(1) =7a(2) =29a(3) =123a(4) =425a(5) =1343a(6) =4197a(7) =12435a(8) =33809a(9) =84663a(10) =198765a(11) =444907a(12) =959801a(13) =2005615a(14) =4064821a(15) =7988867a(16) =15221537a(17) =28122727a(18) =50423741a(19) =87851099a(20) =148962249a(21) =246243487a(22) =397527813a(23) =627798387a(24) =971451697a(25) =1475103511a(26) =2201030157