@n = map { $n + 1 - $_, $_ } 1 .. $n / 2;

##</code><code>##

use integer;
@n = map { $n + 1 - $_, $_ } 1 .. $n / 2;
push @n, $n / 2 + 1 if $n % 2;

##</code><code>##

@n = map { $n + 2 - 2 * $_, 2 * $_ - 1, 2 * $_, $n + 1 - 2 * $_ } 1 .. $n / 4;