Today is 11 day of the year.
11 is prime.
11 is the first non-trivial, palindromic prime.
11 is strictly, non-palindromic.
11 is a Sophie Germain prime and a safe prime, it is therefore a member of the Cunningham chain 2, 5, 11, 23, 47
11 is the fourth lazy caterer number.
11 is a member of the number of leaf nodes in a binary tree.