Index of 3^n within sequence of numbers of form 3^i*5^j.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =10a(5) =14a(6) =19a(7) =24a(8) =30a(9) =37a(10) =44a(11) =52a(12) =61a(13) =70a(14) =80a(15) =91a(16) =102a(17) =114a(18) =127a(19) =140a(20) =154a(21) =169a(22) =185a(23) =201a(24) =218a(25) =236a(26) =254a(27) =273a(28) =293a(29) =313