Smallest k for which k, 2k, ... nk all contain the digit 7.

Terms

a(0) =7a(1) =37a(2) =237a(3) =1789a(4) =4357a(5) =14379a(6) =19587a(7) =93957a(8) =189572a(9) =189572a(10) =189597a(11) =189597a(12) =189597a(13) =1234397a(14) =1839597a(15) =1958798a(16) =1983957a(17) =1983957a(18) =1983957a(19) =1983957a(20) =1983957a(21) =1983957a(22) =3978594a(23) =11983957a(24) =19596487a(25) =29195397a(26) =29195397a(27) =29195397