Find prime n such that reversed n is also prime: Difference between revisions

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(→‎{{header|Phix}}: 1000 is a much better limit)
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Find prime '''n''' for that '''reversed n''' is also prime.
Find prime '''n''' for that '''reversed n''' is also prime.
<br> Let '''0 < n < 500'''
<br> Let '''0 < n < 500'''

=={{header|Phix}}==
<lang Phix>function rp(integer p) return is_prime(to_integer(reverse(sprint(p)))) end function
for n=500 to 1000 by 500 do
sequence res = filter(get_primes_le(n),rp)
string r = join_by(apply(true,sprintf,{{"%3d"},res}),1,14," ")
printf(1,"%d reverse primes < %,d found:\n%s\n",{length(res),n,r})
end for</lang>
{{out}}
<pre>
34 reverse primes < 500 found:
2 3 5 7 11 13 17 31 37 71 73 79 97 101
107 113 131 149 151 157 167 179 181 191 199 311 313 337
347 353 359 373 383 389

56 reverse primes < 1,000 found:
2 3 5 7 11 13 17 31 37 71 73 79 97 101
107 113 131 149 151 157 167 179 181 191 199 311 313 337
347 353 359 373 383 389 701 709 727 733 739 743 751 757
761 769 787 797 907 919 929 937 941 953 967 971 983 991
</pre>


=={{header|Ring}}==
=={{header|Ring}}==

Revision as of 16:27, 19 March 2021

Find prime n such that reversed n is also prime 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 prime n for that reversed n is also prime.
Let 0 < n < 500

Phix

<lang Phix>function rp(integer p) return is_prime(to_integer(reverse(sprint(p)))) end function for n=500 to 1000 by 500 do 

   sequence res = filter(get_primes_le(n),rp)
   string r = join_by(apply(true,sprintf,{{"%3d"},res}),1,14," ")
   printf(1,"%d reverse primes < %,d found:\n%s\n",{length(res),n,r})

end for</lang>

Output:
34 reverse primes < 500 found:
  2   3   5   7  11  13  17  31  37  71  73  79  97 101
107 113 131 149 151 157 167 179 181 191 199 311 313 337
347 353 359 373 383 389

56 reverse primes < 1,000 found:
  2   3   5   7  11  13  17  31  37  71  73  79  97 101
107 113 131 149 151 157 167 179 181 191 199 311 313 337
347 353 359 373 383 389 701 709 727 733 739 743 751 757
761 769 787 797 907 919 929 937 941 953 967 971 983 991

Ring

<lang ring> load "stdlib.ring"

see "working..." + nl

row = 0 num = 0 limit = 500

for n = 1 to limit 

   strm = ""
   strn = string(n)
   for m = len(strn) to 1 step -1
       strm = strm + strn[m]
   next
   strnum = number(strm)
   if isprime(n) and isprime(strnum)
      num = num + 1
      row = row + 1
      see "" + n + " "
      if row%10 = 0
         see nl
      ok
    ok

next

see nl + "found " + num + " primes" + nl see "done..." + nl </lang>

Output:
working...
2 3 5 7 11 13 17 31 37 71 
73 79 97 101 107 113 131 149 151 157 
167 179 181 191 199 311 313 337 347 353 
359 373 383 389 
found 34 primes
done...
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