Number of lucky numbers (A000959) <= 10^n.

Terms

a(0) =1a(1) =4a(2) =23a(3) =153a(4) =1118a(5) =8772a(6) =71918a(7) =609237a(8) =5286238a(9) =46697909a(10) =418348044a(11) =3790060378a(12) =34652117969a(13) =319239995375