#!/usr/athena/bin/perl
#
# usage: ./collatzst.pl (START) (STOP)

use strict;

sub st;
sub cnext;

# get arguments
my $n = shift;
my $nstop = shift;

# defaults.
$nstop = $n, $n = 1 if ($nstop == undef);
$nstop = 100 if ($nstop == undef);

# bounds check
$n = 1 if ($n < 1);
$nstop = 1 if ($nstop < 1);

print $n . "\t" . st ($n++) . "\n" while ($n <= $nstop);

exit;

sub st {

    my $n = shift;
    my $st = 0;
   
    $n = cnext ($n), $st++ while ($n != 1);
    
    return ($st);

}

sub cnext {
    
    my $c = shift;

    if ($c % 2) {
	return (3 * $c + 1);
    } else {
	return ($c / 2);
    }

}