A friend of mine, an USian, says he has seen an SSAN (? Social Security Number?) that had a strange property. Apparently these numbers are 11 digits long. Now here was what was strange/interesting about the number:

1. The number was prime (so far so good, not entirely strange or anything)

2. If you deleted the last two digits (the ones and tens columns) the resulting number was also prime.

3. Delete the next digit along (the former 100s column) and the new number is also a prime.

4. Even with one further deletion, the resulting seven-digit number is prime.

I'm hoping this much info won't reveal what the actual number is. I have no idea what it is but is there the theoretical possibility that only one particular 11-digit number has this property?

If not, is there any way of calculating the 'odds' of this happening? That is, I suppose, asking the question, of how many 11-digit numbers have this property and therefore the odds would be that number out of 10<sup>11</sup>?

Any ideas? I told my friend that this was the maths clever place, so I'm hoping someone can help... :P