I really like the number 1001 because, at first glance to the not-very trained eye like mine, it looks like it should be prime, but in fact it's the product of three consecutive primes:
7 * 11 * 13 = 1001.
(hey, there's another 77 in 7*11

And this reminds me of a math property I once learned as a calculator trick.
If x,y,z be digits and x does not equal zero, then note:
The number xyzxyz divided by 7 divided by 11 divided by 13 = xyz.
Example: 285285 / 7 / 11 / 13 = 285