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

Terms

a(0) =1a(1) =5a(2) =20a(3) =70a(4) =165a(5) =357a(6) =688a(7) =1154a(8) =1867a(9) =2907a(10) =4272a(11) =6070a(12) =8357a(13) =11307a(14) =14998a(15) =19470a(16) =24809a(17) =31211a(18) =38928a(19) =47816a(20) =58201a(21) =70361a(22) =83962a(23) =99648a(24) =117519a(25) =137521a(26) =160270a(27) =185528a(28) =213615a(29) =244649