Find prime n such that reversed n is also prime: Difference between revisions
Find prime n such that reversed n is also prime (view source)
Revision as of 20:21, 14 May 2021
, 3 years agoAda version
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Find prime '''n''' for '''0 < n < 500''' which are also primes when the (decimal) digits are reversed.
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=={{header|Ada}}==
<lang Ada>with Ada.Text_Io;
procedure Reverse_Prime is
type Number is new Long_Integer range 0 .. Long_Integer'Last;
package Number_Io is new Ada.Text_Io.Integer_Io (Number);
function Is_Prime (A : Number) return Boolean is
D : Number;
begin
if A < 2 then return False; end if;
if A in 2 .. 3 then return True; end if;
if A mod 2 = 0 then return False; end if;
if A mod 3 = 0 then return False; end if;
D := 5;
while D * D <= A loop
if A mod D = 0 then
return False;
end if;
D := D + 2;
if A mod D = 0 then
return False;
end if;
D := D + 4;
end loop;
return True;
end Is_Prime;
function Reverse_Num (N : Number) return Number is
N2 : Number := N;
Res : Number := 0;
begin
while N2 /= 0 loop
Res := 10 * Res;
Res := Res + (N2 mod 10);
N2 := N2 / 10;
end loop;
return Res;
end Reverse_Num;
use Ada.Text_Io;
Count : Natural := 0;
begin
for N in Number range 1 .. 499 loop
if Is_Prime (N) and then Is_Prime (Reverse_Num (N)) then
Count := Count + 1;
Number_Io.Put (N, Width => 3); Put (" ");
if Count mod 8 = 0 then
New_Line;
end if;
end if;
end loop;
New_Line;
Put_Line (Count'Image & " primes.");
end Reverse_Prime;</lang>
{{out}}
<pre> 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
34 primes.</pre>
=={{header|ALGOL W}}==
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