palindromic_primes.sf

#!/usr/bin/ruby

# Generate palindromic primes up to a given bound.

# See also:
#   https://oeis.org/A002385      -- Palindromic primes.
#   https://oeis.org/A050251      -- Number of palindromic primes less than 10^n.
#   https://rosettacode.org/wiki/Palindromic_primes

func palindromic_primes(upto, base = 10) {
    var list = []
    for (var p = 2; p <= upto; p = p.next_palindrome(base)) {
        list << p if p.is_prime
    }
    return list
}

say palindromic_primes(1000)

for n in (1..5) {
    var count = palindromic_primes(10**n).len
    say "There are #{count} palindromic primes <= 10^#{n}"
}

__END__
[2, 3, 5, 7, 11, 101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929]

There are 4 palindromic primes <= 10^1
There are 5 palindromic primes <= 10^2
There are 20 palindromic primes <= 10^3
There are 20 palindromic primes <= 10^4
There are 113 palindromic primes <= 10^5
There are 113 palindromic primes <= 10^6
There are 781 palindromic primes <= 10^7
There are 781 palindromic primes <= 10^8
There are 5953 palindromic primes <= 10^9
There are 5953 palindromic primes <= 10^10
There are 47995 palindromic primes <= 10^11
There are 47995 palindromic primes <= 10^12