127

Number
$127$ (one hundred and twenty-seven) is:


 * The $31$st prime number


 * The $4$th Mersenne number and $4$th Mersenne prime after $3, 7, 31$:
 * $127 = 2^7 - 1$


 * The $8$th of $29$ primes of the form $2 x^2 + 29$:
 * $2 \times 7^2 + 29 = 127$