What is 19 and 17?

19

19 is the 8th prime number. It is also a Mersenne prime exponent, meaning 2<sup>19</sup> − 1 is a prime number. In number theory, 19 is related to Fibonacci numbers: specifically, F<sub>19</sub> = 4181. In chemistry, 19 is the atomic number of potassium.

17

17 is the 7th prime number. It is a Fermat prime since it is of the form 2<sup>2<sup>n</sup></sup> + 1 (where n = 2). The regular heptadecagon (17-sided polygon) is constructible with a compass and straightedge, a discovery made by Carl Friedrich Gauss. In mathematics, 17 is the smallest number that is the sum of four distinct squares.