Index of 7^n within the sequence of the numbers of the form 7^i*10^j.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =11a(5) =16a(6) =22a(7) =28a(8) =35a(9) =43a(10) =52a(11) =62a(12) =73a(13) =84a(14) =96a(15) =109a(16) =123a(17) =138a(18) =154a(19) =171a(20) =188a(21) =206a(22) =225a(23) =245a(24) =266a(25) =288a(26) =310a(27) =333a(28) =357a(29) =382