You can start with this, then add in the START number and some error checking ...

#!/usr/bin/perl

use strict;

my $end = $ARGV[0] || 1;
my $sum = 0;

for (1..$end) {
    $sum += $_
}

print "Summation = $sum\n";
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... and some example runs ...

{Z} \\vmware-host\Shared Folders > test
Summation = 1

{Z} \\vmware-host\Shared Folders > test 4
Summation = 10
[download]