use strict;
use warnings;

use List::Util qw( sum );

sub calcIt {
   our $r;
   local $r = sub {
      my ($depth) = @_;
      if ($depth == 0) {
         return sum 1..$_;
      } else {
         return sum map { $r->($depth-1) } 1..$_;
      }
   };

   return $r->(5) for $_[0];
}

print(calcIt(10), "\n");  # 11440
print(calcIt(20), "\n");  # 657800