Circular primes: Difference between revisions
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<pre>First 19 circular primes:
2, 3, 5, 7, 11, 13, 17, 37, 79, 113, 197, 199, 337, 1193, 3779, 11939, 19937, 193939, 199933</pre>
=={{header|Delphi}}==
{{works with|Delphi|6.0}}
{{libheader|SysUtils,StdCtrls}}
Again note how the code is broken up into easy to distinguish subroutines that can be reused, as opposed to mashing everything together into a mass of code that is difficult to understand, debug or enhance.
<syntaxhighlight lang="Delphi">
procedure ShowCircularPrimes(Memo: TMemo);
{Show list of the first 19, cicular primes}
var I,Cnt: integer;
var S: string;
procedure RotateStr(var S: string);
{Rotate characters in string}
var I: integer;
var C: char;
begin
C:=S[Length(S)];
for I:=Length(S)-1 downto 1 do S[I+1]:=S[I];
S[1]:=C;
end;
function IsCircularPrime(N: integer): boolean;
{Test if all rotations of number are prime and}
{A rotation of the number hasn't been used before}
var I,P: integer;
var NS: string;
begin
Result:=False;
NS:=IntToStr(N);
for I:=1 to Length(NS)-1 do
begin
{Rotate string and convert to integer}
RotateStr(NS);
P:=StrToInt(NS);
{Exit if number is not prime or}
{Is prime, is less than N i.e. we've seen it before}
if not IsPrime(P) or (P<N) then exit;
end;
Result:=True;
end;
begin
S:='';
Cnt:=0;
{Look for circular primes and display 1st 19}
for I:=0 to High(I) do
if IsPrime(I) then
if IsCircularPrime(I) then
begin
Inc(Cnt);
S:=S+Format('%7D',[I]);
if Cnt>=19 then break;
If (Cnt mod 5)=0 then S:=S+CRLF;
end;
Memo.Lines.Add(S);
Memo.Lines.Add('Count = '+IntToStr(Cnt));
end;
</syntaxhighlight>
{{out}}
<pre>
2 3 5 7 11
13 17 37 79 113
197 199 337 1193 3779
11939 19937 193939 199933
Count = 19
Elapsed Time: 21.234 ms.
</pre>
=={{header|F_Sharp|F#}}==
This task uses [http://www.rosettacode.org/wiki/Repunit_primes#F.23 rUnitP] and [http://www.rosettacode.org/wiki/Extensible_prime_generator#The_functions Extensible Prime Generator (F#)]
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