Substring primes: Difference between revisions
Added Algol 68
(→{{header|REXX}}: added the computer programming language REXX.) |
(Added Algol 68) |
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Primes (in base ten) in which all substrings are also primes, where '''n < 500'''
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=={{header|ALGOL 68}}==
<lang algol68>BEGIN # find primes where all substrings of the digits are prime #
# reurns a sieve of primes up to n #
PROC sieve = ( INT n )[]BOOL:
BEGIN
[ 1 : n ]BOOL p;
p[ 1 ] := FALSE; p[ 2 ] := TRUE;
FOR i FROM 3 BY 2 TO n DO p[ i ] := TRUE OD;
FOR i FROM 4 BY 2 TO n DO p[ i ] := FALSE OD;
FOR i FROM 3 BY 2 TO ENTIER sqrt( n ) DO
IF p[ i ] THEN FOR s FROM i * i BY i + i TO n DO p[ s ] := FALSE OD FI
OD;
p
END # prime list # ;
# find the primes of interest #
INT max number = 500;
[]BOOL prime = sieve( max number );
FOR p TO UPB prime DO
IF prime[ p ] THEN
INT d := 10;
BOOL is substring := TRUE;
WHILE is substring AND d <= max number DO
INT n := p;
WHILE is substring AND n > 0 DO
INT sub digits = n MOD d;
is substring := IF sub digits = 0 THEN FALSE ELSE prime[ sub digits ] FI;
n OVERAB 10
OD;
d *:= 10
OD;
IF is substring THEN print( ( " ", whole( p, 0 ) ) ) FI
FI
OD
END</lang>
{{out}}
<pre>
2 3 5 7 23 37 53 73 373
</pre>
=={{header|REXX}}==
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