Smallest n-digit triangular number whose external digits as well as internal digits form triangular numbers, or -1 if no such number exists.

A077369

Smallest n-digit triangular number whose external digits as well as internal digits form triangular numbers, or -1 if no such number exists.

Terms

    a(0) =0a(1) =10a(2) =105a(3) =1035a(4) =19900a(5) =162165a(6) =1057785a(7) =10628355a(8) =497086215a(9) =1037196285a(10) =10379451160a(11) =100611783910

External references