for the single line command challenge:

Console.WriteLine("        1\n      121\n    12321\n  1234321\n123454321\n  1234321\n    12321\n      121\n        1");

Of course that violates the "using a loop" constraint :)

Of course you could get a single line instruction and use a loop by preceeding the above with
for (; 1 == 2; ) ;
You can make it a single line in a loop with:
for (int i=0; i < 1; i++)

What was it my professor once said, it's now how efficent you write the code, it's how easy it is to maintain ... LOL