How many 7-card hands can be chosen from a standard deck of 52 cards such that no two cards are of the same rank?

Is it as simple as or am I missing something? I tried starting with all possibilities and then subtracting the set of hands where there was exactly one pair, then exactly 3 the same etc. but it became quite convoluted.

It seems like I am missing a lot of potential hands with as there are four valid choices from each of the 13 ranks each time you choose - not just one.

Would it be:

? but then what would I divide by to remove equivalent permutations?