Question

Let an optimus prime be a prime number whose digit sum is also a prime number. How

many of the first 10 primes are optimus primes?

Answer 1

7

Explanation:

2 = 2 ✓

3 = 3 ✓

5 = 5 ✓

7 = 7 ✓

11 = 1 + 1 = 2 ✓

13 = 1 + 3 = 4 ×

17 = 1 + 7 = 8 ×

19 = 1 + 9 = 10 ×

23 = 2 + 3 = 5 ✓

29 = 2 + 9 = 11 ✓

I hope this helps you :)