 The first few regular numbers are

Several other sequences at OEIS have definitions involving 5-smooth numbers.Although the regular numbers appear dense within the range from 1 to 60, they are quite sparse among the larger integers.A regular number "n" = 2"i"·3"j"·5"k" is less than or equal to "N" if and only if the point ("i","j","k") belongs to the tetrahedron bounded by the coordinate planes and the plane
as can be seen by taking logarithms of both sides of the inequality 2"i"·3"j"·5"k" ≤ "N".