use List::Util qw[ sum ];

$N = 10; 
print sum map{ 
    sum map{ 
        sum map{ 
            sum map{ 
                sum map{ 
                    sum 0 .. $_ 
                } 0 .. $_ 
            } 0 .. $_ 
       } 0 .. $_ 
    } 0 .. $_ 
} 0 .. $N;;
11440

$N = 20; 
print sum map{ 
    sum map{ 
        sum map{ 
            sum map{ 
                sum map{ 
                    sum 0 .. $_ 
                } 0 .. $_ 
            } 0 .. $_ 
        } 0 .. $_ 
    } 0 .. $_ 
} 0 .. $N;;
657800