Why is it hard for me to perform simple mental calculations with certain numbers? [more inside]
posted by lalex on Jun 5, 2007 - 19 answers

A crystal consists of 100,000,000 layers of atoms such that there is 1 atom in the first layer, 3 in the second, 6 in the third, 10 in the fourth, 15 in the fifth, and so forth. Exactly how many atoms are there in the entire crystal? [more inside]
posted by Kwantsar on Oct 8, 2005 - 8 answers

What would a cubic world be like? [more inside]
posted by ac on Feb 17, 2005 - 24 answers