37

Number
$37$ (thirty-seven) is:


 * The $12$th prime number, after $2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31$


 * The $4$th centered hexagonal number after $1, 7, 19$:
 * $37 = 1 + 6 + 12 + 18 = 4^3 - 3^3$


 * The $11$th lucky number:
 * $1, 3, 7, 9, 13, 15, 21, 25, 31, 33, 37, \ldots$


 * The $4$th emirp after $13, 17, 31$.


 * The $2$nd integer which has a reciprocal whose period is $3$:
 * $\dfrac 1 {37} = 0 \cdotp \dot 02 \dot 7$


 * The $5$th of $5$ primes of the form $2 x^2 + 5$:
 * $2 \times 4^2 + 5 = 37$


 * The $3$rd of $29$ primes of the form $2 x^2 + 29$:
 * $2 \times 2^2 + 29 = 37$

Also see

 * Period of Reciprocal of 37 has Length 3