a(n) = triangular number whose index is the concatenation of the first n natural numbers.

A077694

a(n) = triangular number whose index is the concatenation of the first n natural numbers.

Terms

    a(0) =1a(1) =78a(2) =7626a(3) =761995a(4) =76205685a(5) =7620753696a(6) =762078456028

External references