a(n) is the number of positive integers <= 10^n that are divisible by no prime exceeding 3.

Terms

a(0) =1a(1) =7a(2) =20a(3) =40a(4) =67a(5) =101a(6) =142a(7) =190a(8) =244a(9) =306a(10) =376a(11) =452a(12) =534a(13) =624a(14) =720a(15) =824a(16) =935a(17) =1052a(18) =1178a(19) =1309a(20) =1447a(21) =1593a(22) =1745a(23) =1905a(24) =2071a(25) =2244a(26) =2424a(27) =2611a(28) =2806a(29) =3006