What is the sum of the first four prime numbers?

A prime number is a natural number greater than 1 that has exactly two positive divisors: 1 and itself. A number with more than two divisors is called composite, and 1 itself is neither prime nor composite. Listed in increasing order, the prime numbers begin 2, 3, 5, 7, 11, 13, …

1. 2 is the first prime number — it is the only even prime, since every other even number has 2 as an additional divisor.

2. 3 is the second prime number — its only divisors are 1 and 3.

3. 4 is skipped because it divides evenly by 2 as well as 1 and 4, so it is composite; the third prime number is therefore 5, whose only divisors are 1 and 5.

4. 6 is skipped because it divides evenly by 1, 2, 3, and 6; the fourth prime number is therefore 7, whose only divisors are 1 and 7.

5. Adding these four primes: 2 + 3 + 5 + 7 = 17.

Cross-check by adding sequentially: 2 + 3 = 5; 5 + 5 = 10; 10 + 7 = 17 — the same total, confirming the sum.

So, the sum of the first four prime numbers is 17.