Question

The sum of two consecutive triangular numbers gives a __ number.

Answer 1

Triangular numbers are any of the series of numbers (1, 3, 6, 10, 15, etc.) obtained by continued summation of the natural numbers 1, 2, 3, 4, 5, etc. $\begin{array}{ccccccc}1& 2& 3& 4& 5& 6& 7\\ 1& 1+2& 1+2+3& 1+2+3+4& 1+2+3+4+5& 1+2+3+4+5+6& 1+2+3+4+5+6+7\end{array}$