The Walrii Prime

[Yuki]

I just found a pretty interesting prime here:

Code Select Expand

222227772222222222222222222272227277222222222222222722222722722222222222227227727222272222222222227272277722227722222222227722272272227272222222227722272227227227222222272272272227272227222222272227727272722222722222772722222777222222722222727772272222222222722222722727772222222222272222722722272222222222272222722722272222222222272222722722272222222222272222727722272222222222272222727772722272222222227222727272722722272222227722727772722222227222222772277272722222222722722722277227222722222722722272272222777272222272272227272277222777722277727772277722222222277772222777

Or, if you rearrange it in a square:

222227772222222222222222
222272227277222222222222
222722222722722222222222
227227727222272222222222
227272277722227722222222
227722272272227272222222
227722272227227227222222
272272272227272227222222
272227727272722222722222
772722222777222222722222
727772272222222222722222
722727772222222222272222
722722272222222222272222
722722272222222222272222
722722272222222222272222
727722272222222222272222
727772722272222222227222
727272722722272222227722
727772722222227222222772
277272722222222722722722
277227222722222722722272
272222777272222272272227
272277222777722277727772
277722222222277772222777

As far as I know, this 576-digit number is prime (or have high probabilities to be prime according to the GNU Multiple Precision (GMP) library, someone should independently verify if you have a copy of Mathematica or something just checked with Wolfram Cloud, it's prime). Now if you want to Ctrl-F this page and search for 7...

Now you wonder how the hell I did that? It's a secret~

Code (PHP) Select Expand


<?php
// By [email protected]
// Licensed under LiLiQ-R
$im = imagecreatefromgif($argv[1]);
$ix = imagesx($im);
$iy = imagesy($im);
function findprime($a,$b)
{
  global $im,$ix,$iy;
  $s="";
  for($y=0; $y<$iy; $y++)
  {
    for($x=0; $x<$ix; $x++)
    {
      $c=imagecolorat($im,$x,$y);
      $s.=($c>0)?$a:$b;
    }
  }
  return gmp_nextprime($s);
}
$r=array();
for($a=1;$a<=9;$a++)
{
  for($b=0;$b<=9;$b++)
  {
    $n = findprime($a,$b);
    $p = count(array_unique(str_split(gmp_strval($n))));
    //echo $a." ".$b/*." ".gmp_sub($n, $s)*/." ".$p."\n";
    if($p==2)
    {
      $z=array();
      $z[]=$a;
      $z[]=$b;
      $r[]=$z;
    }
  }
}
for($i=0;$i<count($r);$i++)
{
  echo $m=gmp_strval(findprime($r[$i][0],$r[$i][1]))."\n";
  echo chunk_split($m,$ix);
}


You must have GMP and GD installed in your PHP installation. Script should take about 45 seconds to run.

[close]

Of course, some of you will recognize the fact I was inspired by this video:

[JWinslow23]

I didn't think you'd actually do it! Or that it'd be so "clean" once someone found it (this is a literal perfect representation of the , no extraneous or "wrong" digits).

Nice job, dude!

[kotu]

nice code

[Yuki]

Yeah, I'm kinda surprised I'd even find something. Actually, the last 3 digits are wrong, but of all the combinations of white and black pixels I tried, this was the only one that fits with the rest with no random digits.

[kotu]

We still believe it's a prime

Thanks juju

[_iPhoenix_]

Dammit.

My [crappy, written in like 5 min to brute force the hell out of this problem] C code is still running. (It's been like 2 days, too)

I guess I'll let it keep running and see if it comes up with anything different.