Hmm. 6615?

What I mean is, I think it is *quite likely* to be 6615, but that's on the basis of noting a pattern that applies to some but not all of the other numbers.

Ah, yes, that makes sense. I factored the numbers, but didn't think to count factors. And many of the numbers are of the form

x * 15 * 21 (for 11, 13, 17, 19) though the others aren't...

and 6615 is 21 x 15 x 21 (or 3^3*5*7^2)

I will grant you that this is not a perfect approach. Hence the question mark.

I am now quite surprised that I managed to factor all the numbers without checking the number of factors or considering that the large number of odd factors might be relevant.

6435+450+240=7125