ways of calculating the sum of 1 to n

sum_algorithms.pl

#!/usr/bin/env perl

use strict;
use warnings;
use feature 'say';

# To extend this to infinity, read:
# https://medium.com/cantors-paradise/the-ramanujan-summation-1-2-3-1-12-a8cc23dea793

# For loop
sub v1_sum_one_to_n {
    my $n = shift;

    my $sum = 0;
    foreach my $num (1 .. $n) {
        $sum += $num;
    }

    return $sum;
}


# recursion
sub v2_sum_one_to_n {
    my $n = shift;

    return 1 if $n == 1;
    return return $n + v2_sum_one_to_n($n-1);
}

# mathematics
sub v3_sum_one_to_n {
    my $n = shift;
    return $n * ($n + 1) / 2;
}

my $num = $ARGV[0];
die "Invald arg $num" unless $num && $num > 0 && int($num) == $num;


say "For loop: "    . v1_sum_one_to_n($num);
say "Recursion: "   . v2_sum_one_to_n($num);
say "Mathematics: " . v3_sum_one_to_n($num);