use strict;
use warnings;

my $A1;
my $A2;
my $A3;
my $A4;
my $X16;
my $SUM;
my $PI = 0;

print "\n\nThis program calculates the value of PI using the BBP formula, which was",
"\ndiscovered in 1995 by Canadian mathematician Simon Plouffe.\n";

for (my $i = 0; $i < 18; $i++)
{
   $A1 = 4 / (8 * $i + 1);
   $A2 = 2 / (8 * $i + 4);
   $A3 = 1 / (8 * $i + 5);
   $A4 = 1 / (8 * $i + 6);
   $X16 = (1 / 16) ** $i;
   $SUM = ($A1 - $A2 - $A3 - $A4) * $X16;
   $PI += $SUM;
   print "\n i = $i\t\t$SUM";
}
print "\n\n\t   PI = $PI\n";