A Beatty sequence: floor( n * (1 + sqrt(3))/2 ).

Terms

a(0) =1a(1) =2a(2) =4a(3) =5a(4) =6a(5) =8a(6) =9a(7) =10a(8) =12a(9) =13a(10) =15a(11) =16a(12) =17a(13) =19a(14) =20a(15) =21a(16) =23a(17) =24a(18) =25a(19) =27a(20) =28a(21) =30a(22) =31a(23) =32a(24) =34a(25) =35a(26) =36a(27) =38a(28) =39a(29) =40