Re^2: Diamonds for fun

[a]

Had to:

perl -e '$n=pop; print "\n", " "x($n-$_),1..$_,reverse 1..$_-1, for 1.
+.$n,reverse 1..$n-1'  9

for 5.8 ish ... seems like there's a marvelous recursive solution but my brain is too small to find it.