121

Number
$121$ (one hundred and twenty-one) is:


 * $11^2$


 * The $11$th square number after $1, 4, 9, 16, 25, 36, 49, 64, 81, 100$:
 * $121 = 11 \times 11$


 * The second square number after $25$ of the form $n! + 1$:
 * $121 = 5! + 1 = 11^2$
 * where $!$ denotes the factorial function.


 * $121$ is a palindromic number whose square is also palindromic:

Also see

 * Brocard's Problem
 * Square of Small-Digit Palindromic Number is Palindromic