A student and I were playing with determinants recently and we stumbled upon an amusing one. I have a very strong feeling that this must have been stumbled upon many times in the past so we’re making no claim to originality. All we’re claiming is that if you haven’t seen this before, you might be in for a little amusement.
Let 
Compute the determinant of 
In other words, if you write out Pascal’s triangle as a grid instead of a triangle as shown below, then
If you’ve seen this before, please let us know where.
Girls' Angle 
Nice!
This is the pascal matrix with k=1. It has a nice inverse when k is a reciprocal of an integer.
Thank you for identifying it!
Googling “Pascal Matrix” brought me to the nice Wikipedia entry which references a nice Monthly article by Edelman and Strang, Pascal Matrices.