I don't know, but I just discovered that Amazon has the 36-pencil set for the same price as the 24-pencil set. Must be a mistake in their pricing. It was just enough to push me over the edge, as I have been wanting to try out the Inktense pencils for a long time. Here is the link:
https://www.amazon.com/gp/product/B001U3QO7O/