a(n) is the largest triangular number that is the concatenation of two n-digit numbers 2*x and x.

A380792

a(n) is the largest triangular number that is the concatenation of two n-digit numbers 2*x and x.

Terms

    a(0) =21a(1) =9045a(2) =890445a(3) =88904445a(4) =8889044445a(5) =888890444445

External references