17

Number
$17$ (seventeen) is:


 * The $7$th prime number, after $2, 3, 5, 7, 11, 13$


 * The $3$rd Fermat prime, after $3, 5$:
 * $17 = 2^{2^2} + 1$


 * The smallest integer to be the sum of $2$ distinct powers of $4$:
 * $17 = 1 + 16 = 1^4 + 2^4$


 * The only prime number to equal the sum of the digits of its cube:
 * $17 = 4 + 9 + 1 + 3$, while $17^3 = 4913$

Also see

 * Construction of Regular Heptadecagon