Indices of triangular numbers in A087359.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =6a(5) =8a(6) =12a(7) =59a(8) =72a(9) =812a(10) =1523a(11) =47051a(12) =234380a(13) =82528328a(14) =963837743