Let M be any 3 × 3 matrix with entries from the set {0, 1, 2}. Then maximum number of such matrices, for which the sum of diagonal elements of MTM is seven, is ______

abcdefghiadgbehcfi=a2+b2+c2+d2+e2+f2+g2+h2+i2=7 Case I : Seven (1's) and two (0's)  9C2=36and Case- II : One (2) and three (1’s) and five (0’s) - 9!5!3!=504Therefore, total is 36+504=540