CIRCLE WITH A DOT

Combinatorics can be a bit weird sometimes: the number of ways to arrange N Tetris pieces into a 2-by-2N rectangle is the Nth Fibonacci number squared.

@ruuddotorg argh, I think you have to divide the 24 orientations for (2) by some symmetry factor. I'm guessing in half but need to double-check...EDIT: yeah, I think it's 12. you can generate them uniquely by starting with 2 pancakes (3 options) and then choosing one of the four corners in in the plane of their orientation to swap between the two pancakes. 3 * 4 = 12.if this is right, that's 12+3+1 = 16 disconnected tetracube decompositions.