a(n) is the number of distinct products b_1*b_2*...*b_n where 1 <= b_i <= n.

Terms

a(0) =1a(1) =3a(2) =10a(3) =25a(4) =91a(5) =196a(6) =750a(7) =1485a(8) =3025a(9) =5566a(10) =23387a(11) =38402a(12) =163268a(13) =284376a(14) =500004a(15) =795549a(16) =3575781a(17) =5657839a(18) =25413850a(19) =40027130a(20) =66010230a(21) =105164280a(22) =490429875a(23) =713491350a(24) =1232253906