foreach my $n (1..1000) {
 $x=.5*$n*($n+1);
 print $x;
}

##</code><code>##

#!/usr/bin/perl
use strict;


my @words=('ONE', 'THREE', 'SIX', 'TEN');
my %letters;
foreach (@words) {
 my @a=split //, $_;
 foreach (@a) {
  $letters{$_}=0;
 }
}

#Construct an array of the letters (you'll see why 
#in a few lines)
my @letters=(keys %letters);

my $count;
my $oldtime;
do {
$letters{$letters[$#letters]}++;
foreach( reverse(0..$#letters)) {
 if ($count++>10000) {
  print time-$oldtime,"\n";
  $oldtime=time;
  $count=0;
 }
#Increment the number for the letter at the end
#of the array, and don't forget to carry
 if ($letters{$letters[$_]} > 9) {
  $letters{$letters[$_]}=0;
  $letters{$letters[$_-1]}++;
 }
#Turn the letters into numbers
 prep(%letters);
}
} until ($letters{$letters[0]} > 9);
 


sub prep {
 my %letters=@_;
 my $match=0;
 my %match;
  foreach my $a (@words) {
   my $test= $a;
#Change the letters into numbers
   foreach (keys %letters) {
    $test=~ s/$_/$letters{$_}/g;
   }
   $match{"$a=$test is triangular\n"}=1 and $match ++ if is_triangular($test);
  }
  if ($match>0) {
  # print "-----------\n";
   if ($match>(@words-1)) {
    print $_ foreach keys %match;
    print "Found it!\n";
    #exit;
   }
  }

}


#This should be memoised, but I'm afraid of the
#memory blowout
sub is_triangular {
 my $num=shift;
 my ($n,$x)=(1,0);
 do {
  $x=.5*$n*(++$n);
  return 1 if $x==$num;
 } until $x > $num;
 return 0;
}