Index of 4^n within the sequence of the numbers of the form 4^i*7^j.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =10a(5) =14a(6) =19a(7) =24a(8) =30a(9) =37a(10) =45a(11) =53a(12) =62a(13) =72a(14) =82a(15) =93a(16) =105a(17) =118a(18) =131a(19) =145a(20) =160a(21) =175a(22) =191a(23) =208a(24) =226a(25) =244a(26) =263a(27) =283a(28) =303a(29) =324