Triangular numbers composed of digits {1,2,3}.

Terms

a(0) =1a(1) =3a(2) =21a(3) =231a(4) =2211a(5) =3321a(6) =21321a(7) =32131a(8) =222111a(9) =232221a(10) =11132121a(11) =22221111a(12) =22321221a(13) =2222211111a(14) =2223211221a(15) =12221332311a(16) =222222111111a(17) =222232111221