a(n) = floor(volume of 4-sphere of radius n).

Terms

a(0) =0a(1) =4a(2) =78a(3) =399a(4) =1263a(5) =3084a(6) =6395a(7) =11848a(8) =20212a(9) =32377a(10) =49348a(11) =72250a(12) =102328a(13) =140942a(14) =189575a(15) =249824a(16) =323407a(17) =412159a(18) =518035a(19) =643108a(20) =789568a(21) =959725a(22) =1156007a(23) =1380959a(24) =1637248a(25) =1927657a(26) =2255086a(27) =2622556a(28) =3033205a(29) =3490291