Smallest k for which k, 2k, ... nk all contain the digit 4.

Terms

a(0) =4a(1) =24a(2) =47a(3) =471a(4) =487a(5) =1248a(6) =1249a(7) =6248a(8) =6249a(9) =6249a(10) =12493a(11) =12493a(12) =12493a(13) =12493a(14) =12498a(15) =31249a(16) =62499a(17) =62499a(18) =62499a(19) =62499a(20) =62499a(21) =62499a(22) =62499a(23) =62499a(24) =62499a(25) =62499a(26) =62499a(27) =62499a(28) =62499a(29) =62499