Repunit primes: Difference between revisions

=={{header|ALGOL 68}}==

{{works with|ALGOL 68G|Any - tested with release 2.8.3.win32}}

<syntaxhighlight lang="algol68">

BEGIN # find repunit (all digits are 1 ) primes in various bases #

INT max base = 16;

INT max repunit digits = 1000;

PR precision 3000 PR # set precision of LONG LONG INT #

# 16^1000 has ~1200 digits but the primality test needs more #

PR read "primes.incl.a68" PR # include prime utilities #

[]BOOL prime = PRIMESIEVE max repunit digits;

FOR base FROM 2 TO max base DO

LONG LONG INT repunit := 1;

print( ( whole( base, -2 ), ":" ) );

FOR digits TO max repunit digits DO

IF prime[ digits ] THEN

IF is probably prime( repunit ) THEN

# found a prime repunit in the current base #

print( ( " ", whole( digits, 0 ) ) )

FI

FI;

repunit *:= base +:= 1

OD;

print( ( newline ) )

OD

END

</syntaxhighlight>

{{out}}

<pre>

2: 2 3 5 7 13 17 19 31 61 89 107 127 521 607

3: 3 7 13 71 103 541

4: 2

5: 3 7 11 13 47 127 149 181 619 929

6: 2 3 7 29 71 127 271 509

7: 5 13 131 149

8: 3

9:

10: 2 19 23 317

11: 17 19 73 139 907

12: 2 3 5 19 97 109 317 353 701

13: 5 7 137 283 883 991

14: 3 7 19 31 41

15: 3 43 73 487

16: 2

</pre>