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 $5$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 $2 x^2 + 29$:
 * $2 \times 2^2 + 29 = 37$