15 If $m, n \in\left\{x \mid x=a_{2} \times 10^{2}+a_{1} \times 10+a_{0}\right\}$, where $a_{i} \in\{1,2,3, 4,5,6,7\}, i=0,1,2$, and $m+n=636$, then the number of distinct points $(m, n)$ representing points on the plane is $\qquad$
(15) 90 .