Index of 9^n within the sequence of the numbers of the form 5^i*9^j.

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =17a(5) =24a(6) =33a(7) =43a(8) =54a(9) =67a(10) =81a(11) =97a(12) =114a(13) =132a(14) =152a(15) =173a(16) =195a(17) =219a(18) =244a(19) =270a(20) =298a(21) =327a(22) =358a(23) =390a(24) =423a(25) =458a(26) =494a(27) =531a(28) =570a(29) =610