Any larger pairs after this?

Computer Science Level 2

$\begin{aligned} 1 + 2 + \cdots + 10 &= 1^2 + 2^2 + \cdots + 5^2\\ 1 + 2 + \cdots + 13 &= 1^2 + 2^2 + \cdots + 6^2 \\ &\vdots \end{aligned}$

Find the next pair of integers $(M,N)$ larger than $(13,6)$ such that $1 + 2 + \cdots +M= 1^2 + 2^2 + \cdots + N^2.$ Submit your answer as $M+N$ .