Markoff numbers (A002559) multiplied by 3.

Terms

a(0) =3a(1) =6a(2) =15a(3) =39a(4) =87a(5) =102a(6) =267a(7) =507a(8) =582a(9) =699a(10) =1299a(11) =1830a(12) =2955a(13) =3975a(14) =4791a(15) =8691a(16) =12543a(17) =17223a(18) =19398a(19) =22683a(20) =27231a(21) =32838a(22) =44103a(23) =85971a(24) =100383a(25) =112998a(26) =129783a(27) =154923a(28) =186630a(29) =225075