Terms of A181666 of the form 3*k+1.

Terms

a(0) =1a(1) =4a(2) =10a(3) =16a(4) =40a(5) =64a(6) =85a(7) =160a(8) =256a(9) =340a(10) =640a(11) =682a(12) =1024a(13) =1360a(14) =2560a(15) =2728a(16) =4096a(17) =5440a(18) =5461a(19) =10240a(20) =10912a(21) =16384a(22) =21760a(23) =21844a(24) =40960a(25) =43648a(26) =43690a(27) =65536a(28) =87040a(29) =87376