a(n)^3 is smallest cube containing exactly n 5's.

Terms

a(0) =5a(1) =25a(2) =136a(3) =715a(4) =1526a(5) =11828a(6) =8121a(7) =115798a(8) =319405a(9) =1771087a(10) =2179693a(11) =11665419a(12) =38160335a(13) =176024528a(14) =1367063798a(15) =3257101805a(16) =9109186828a(17) =38598478444a(18) =136736651535a(19) =380814792667a(20) =821922685008