Triangular numbers written backwards.

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =1a(5) =51a(6) =12a(7) =82a(8) =63a(9) =54a(10) =55a(11) =66a(12) =87a(13) =19a(14) =501a(15) =21a(16) =631a(17) =351a(18) =171a(19) =91a(20) =12a(21) =132a(22) =352a(23) =672a(24) =3a(25) =523a(26) =153a(27) =873a(28) =604a(29) =534