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sub f {
#234567890123456789012345678901234567890123456789012345678901234567890
+12345678901
my$x=my$i=pop;$x?([1..$x],map[(map$_+2*$x-1,reverse@$_),++$i],reverse 
+f($x-1)):()
}

## print "@$_\n" for f(5);
1 2 3 4 5
...
15 24 25 20 7
14 23 22 21 8
13 12 11 10 9

 +---------------+
 | 1 2 3 ...  n  |
...
 | |       |  .  |
 | +-------+ 2n-1|
 +---------------+