54

7+47 = 54

7x47 = 329

What is so cool about that? Well 54 raised to the power 54 (that's 54 times itself 54 times) is the highest power of 54 that divides 329 factorial (that is 329 factorial is divisible by 54 to the 54th).

In symbols:

54^54 divides 329!

54^55 does not divide 329!