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M(n) is the array in which m(x,y,z,t, w)=x*y*z*t*w for x = 1 to n, y = 1 to n, z = 1 to n, t = 1 to n and w = 1 to n. In M(7) the most frequently occurring numbers are 360, 420, 504 and 840. They occur 300 times, so a(7) = 300.