a(n) = floor(n*(sqrt(5)+5)/2).

Terms

a(0) =3a(1) =7a(2) =10a(3) =14a(4) =18a(5) =21a(6) =25a(7) =28a(8) =32a(9) =36a(10) =39a(11) =43a(12) =47a(13) =50a(14) =54a(15) =57a(16) =61a(17) =65a(18) =68a(19) =72a(20) =75a(21) =79a(22) =83a(23) =86a(24) =90a(25) =94a(26) =97a(27) =101a(28) =104a(29) =108