What makes the number interesting?
Obviously there will be many answers to this. Here are a couple of special things about which have turned up in my first year module recently (and in one case this was unplanned!)
- is the only square number which is exactly one more than a prime number
- is the only positive integer such that is not prime, and yet is not divisible by . (Here we follow the convention that .)
Do you have any other favourite exceptional properties of ?