26

Since today is my daughter's 26th birthday, here is some information on the number 26:

26 is the only integer sandwiched just above a square (25) and just below a cube (27).

26 is the smallest non-palindromic number whose square is palindromic: 26^2 = 676

26 is the smallest number with three representations as a sum of three distinct primes: 26 = 2 + 5 + 19 = 2 + 7 + 17 = 2 + 11 + 13.

There are 26 letters in the English alphabet.

There are 26 spacetime dimensions in bosonic string theory. 

26 is the gematric number of the name of G-d, the sum of the Hebrew characters of the Tetragrammaton י-הוה

26 is a 2003 novel by Leo McKay, Jr.

26 is the name of the Australian Alternative Rock band.

26 is the smallest number that can be expressed by three identical prime digits in a prime base, i.e., 222 in base three. Note that it is also the reverse of the second such number: 62 = 222 in base 5.