Sum of two adjacent numbers are primes

Sum of two adjacent numbers are primes is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Task

Show on this page the first 20 numbers and sum of two adjacent numbers which sum is prime.

Ring

<lang ring> load "stdlibcore.ring" see "working..." + nl n = 0 num = 0

while true

    n++
    sum = 2*n+1
    if isprime(sum)
       num++
       if num < 21
         ? "n = " + n + "  sum= " + sum
       else
         exit
       ok
     ok

end

see "done..." + nl </lang>

Output:

working...
n = 1  sum= 3
n = 2  sum= 5
n = 3  sum= 7
n = 5  sum= 11
n = 6  sum= 13
n = 8  sum= 17
n = 9  sum= 19
n = 11  sum= 23
n = 14  sum= 29
n = 15  sum= 31
n = 18  sum= 37
n = 20  sum= 41
n = 21  sum= 43
n = 23  sum= 47
n = 26  sum= 53
n = 29  sum= 59
n = 30  sum= 61
n = 33  sum= 67
n = 35  sum= 71
n = 36  sum= 73
done...