##[Pyke](http://pyke.catbus.co.uk), 6 bytes, [Cracked](http://codegolf.stackexchange.com/a/77478/32686)

 ###X#s
Output:

 a(2) = 8
 a(8) = 80
 a(10) = 120

This doesn't work with N<1

Original solution:

 hSmX$s