Given,
f(mn)=f(m)⋅f(n)
Put m=1, then f(1⋅n)=f(1)⋅f(n)⇒f(1)=1f(n)=0
Put m=n=2
f(4)=f(2)⋅f(2)
If f(2)=1, then f(4)=1 and if f(2)=2, then f(4)=4
Put m=2,n=3
f(6)=f(2)⋅f(3)
If f(2)=1, then f(3) can be any value between 1 to 7
If f(2)=2, then f(3) can be 1 or 2 or 3
Similarly f(5),f(7) can take any value from 1,2,...,7
So, total number of function =(1×1×7×1×7×1×7)+(1×1×3×1×7×1×7)
=490