Index of 7^n within the sequence of the numbers of the form 7^i*9^j.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =11a(5) =16a(6) =22a(7) =29a(8) =37a(9) =45a(10) =54a(11) =64a(12) =75a(13) =87a(14) =100a(15) =114a(16) =129a(17) =145a(18) =161a(19) =178a(20) =196a(21) =215a(22) =235a(23) =256a(24) =278a(25) =301a(26) =325a(27) =349a(28) =374a(29) =400