Neither == 0 (mod 4) nor a power of 3.

Terms

a(0) =1a(1) =2a(2) =5a(3) =6a(4) =7a(5) =10a(6) =11a(7) =13a(8) =14a(9) =15a(10) =17a(11) =18a(12) =19a(13) =21a(14) =22a(15) =23a(16) =25a(17) =26a(18) =29a(19) =30a(20) =31a(21) =33a(22) =34a(23) =35a(24) =37a(25) =38a(26) =39a(27) =41a(28) =42a(29) =43