Primes whose first and last number is 3

Primes whose first and last number is 3 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

Find primes n whose first and last number is 3, where n < 4,000

Ring

<lang ring> load "stdlib.ring" see "working..." + nl see "Primes whose first and last number is 3" + nl row = 0

for n = 1 to 4000

   strn = string(n)
   if left(strn,1) = "3" and right(strn,1) = "3" and isprime(n)
      see "" + n + " "
      row++
      if row%5 = 0
         see nl
      ok
   ok

next

see nl + "Found " + row + " numbers" + nl see "done..." + nl </lang>

Output:

working...
Primes whose first and last number is 1
3 313 353 373 383 
3023 3083 3163 3203 3253 
3313 3323 3343 3373 3413 
3433 3463 3533 3583 3593 
3613 3623 3643 3673 3733 
3793 3803 3823 3833 3853 
3863 3923 3943 
Found 33 numbers
done...

XPL0

<lang XPL0>func IsPrime(N); \Return 'true' if N is a prime number int N, I; [if N <= 1 then return false; for I:= 2 to sqrt(N) do

   if rem(N/I) = 0 then return false;

return true; ];

func Has3s(N); \Return 'true' if first and last digits are 3 int N; [N:= N/10; if rem(0) # 3 then return false; while N do N:= N/10; return rem(0) = 3; ];

int Count, N; [Count:= 0; for N:= 0 to 4000-1 do

   if Has3s(N) & IsPrime(N) then
       [IntOut(0, N);
       Count:= Count+1;
       if rem(Count/10) = 0 then CrLf(0) else ChOut(0, 9\tab\);
       ];

CrLf(0); IntOut(0, Count); Text(0, " such primes found below 4000. "); ]</lang>

Output:

3       313     353     373     383     3023    3083    3163    3203    3253
3313    3323    3343    3373    3413    3433    3463    3533    3583    3593
3613    3623    3643    3673    3733    3793    3803    3823    3833    3853
3863    3923    3943    
33 such primes found below 4000.