First (leftmost) digit - second digit + third digit - fourth digit .... = 12.

Terms

a(0) =309a(1) =408a(2) =419a(3) =507a(4) =518a(5) =529a(6) =606a(7) =617a(8) =628a(9) =639a(10) =705a(11) =716a(12) =727a(13) =738a(14) =749a(15) =804a(16) =815a(17) =826a(18) =837a(19) =848a(20) =859a(21) =903a(22) =914a(23) =925a(24) =936a(25) =947a(26) =958a(27) =969a(28) =3090a(29) =4080