Ternary sieve: delete every 3rd number, then every 9th, 27th, etc.

Terms

a(0) =1a(1) =2a(2) =4a(3) =5a(4) =7a(5) =8a(6) =10a(7) =11a(8) =14a(9) =16a(10) =17a(11) =19a(12) =20a(13) =22a(14) =23a(15) =25a(16) =28a(17) =29a(18) =31a(19) =32a(20) =34a(21) =35a(22) =37a(23) =38a(24) =41a(25) =43a(26) =46a(27) =47a(28) =49a(29) =50