Definitions
In mathematics, additive primes are prime numbers for which the sum of their decimal digits are also primes.



Task
Write a program to determine (and show here) all additive primes less than 500.

Optionally, show the number of additive primes.



Also see

   the OEIS entry:   A046704 additive primes.
   the prime-numbers entry:   additive primes.
   the geeks for geeks entry: additive prime number.
   the prime-numbers fandom: additive primes.


require "prime"
 
additive_primes = Prime.lazy.select{|prime| prime.digits.sum.prime? }
 
N = 500
res = additive_primes.take_while{|n| n < N}.to_a
puts res.join(" ")
puts "\n#{res.size} additive primes below #{N}."
 