M(-9,15) and N (-7,3) with solutions

(m2 - n2) - 2mn = 7 as (m - n)2 - 2n2 = 7. The equation x2 - 2y2 = 7 is satisfied by (lxi, Iyl)] = (3,1), (13,9), (75,53), and these yield the triples (-3, 4, 5), (8, 15, 17), ...