Rebol3 Code Examplex

Concatenate two primes is also prime

Find pairs of primes p1,p2 (e.g., below a bound like 100) such that their decimal concatenation is also prime.

Rebol [
    title: "Rosetta code: Concatenate two primes is also prime"
    file:  %Concatenate_two_primes_is_also_prime.r3
    url:   https://rosettacode.org/wiki/Concatenate_two_primes_is_also_prime
]

print as-yellow "Concatenated-pair primes from primes < 100:^/"
primes: collect [ for i 2 99 1 [ if prime? i [keep i]] ]
primes: sort unique collect [
    foreach p1 primes [
        foreach p2 primes [
            if prime? n: to integer! ajoin [p1 p2] [
                keep n
            ]
        ]
    ]
]
i: 1 foreach p primes [
    prin pad p 5
    if zero? ++ i % 16 [prin LF]
]

print ["^/Found" as-green length? primes "concatenated primes."]

Output:

Concatenated-pair primes from primes < 100:

23   37   53   73   113  137  173  193  197  211  223  229  233  241  271  283  
293  311  313  317  331  337  347  353  359  367  373  379  383  389  397  433  
523  541  547  571  593  613  617  673  677  719  733  743  761  773  797  977  
1117 1123 1129 1153 1171 1319 1361 1367 1373 1723 1741 1747 1753 1759 1783 1789 
1913 1931 1973 1979 1997 2311 2341 2347 2371 2383 2389 2917 2953 2971 3119 3137 
3167 3719 3761 3767 3779 3797 4111 4129 4153 4159 4337 4373 4397 4723 4729 4759 
4783 4789 5323 5347 5923 5953 6113 6131 6143 6173 6197 6719 6737 6761 6779 7129 
7159 7331 7919 7937 8311 8317 8329 8353 8389 8923 8929 8941 8971 9719 9743 9767 

Found 128 concatenated primes.