a(n) = floor( (4/3)*Pi*n^3 ).

Terms

a(0) =0a(1) =4a(2) =33a(3) =113a(4) =268a(5) =523a(6) =904a(7) =1436a(8) =2144a(9) =3053a(10) =4188a(11) =5575a(12) =7238a(13) =9202a(14) =11494a(15) =14137a(16) =17157a(17) =20579a(18) =24429a(19) =28730a(20) =33510a(21) =38792a(22) =44602a(23) =50965a(24) =57905a(25) =65449a(26) =73622a(27) =82447a(28) =91952a(29) =102160