a(n)^3 is smallest cube containing exactly n 6's.

Terms

a(0) =4a(1) =55a(2) =36a(3) =716a(4) =1188a(5) =4055a(6) =13832a(7) =18821a(8) =190806a(9) =1542023a(10) =3971816a(11) =13881356a(12) =55009989a(13) =154057624a(14) =551727536a(15) =1881662989a(16) =4014051821a(17) =15448244536a(18) =185043243523a(19) =405480132286a(20) =550651031786