Clone Project: Spell Progression II

I worked for days on trying to come up with a simple formula for the Magic-User spell progression. The one presented previously was the simplest one of several I considered.

Simplest, that is, from the perspective of "How many spells can I cast at Level X?" There is a way to maybe make it simpler, by looking at it from a different perspective: "At what level can I add another spell of Level Y to the number I can cast?" It's a matter of whether you look up your class level first or the spell level first; the first method, when put in table form, requires reading one line, while the second method in table form would have one line per spell level, something like this:

	# of spells
Spell Level	per level:	1	2	3	4
I		1	2	3	4
II		3	4	7	10
III		5	6	9	12
IV		7	8	11	14
V		9	10	12	14
VI		11	12	13	14

Or, putting it into a shorter, formula format:

Magic-Users can prepare and cast two spells of a given spell level when their caster level is double the spell level, or one spell of double the spell level - 1. They add a third and fourth spell at:

• 3rd and 4th level, for 1st level spells;
• every three levels after (2 x spell level), for 2nd through 4th level spells;
• every two levels after (2 x spell level), for 5th level spells;
• every level after 12th, for 6th level spells.

On the cheat sheet, there would be some kind of abbreviated version of the six-line table above.

Edit: I wrote "half" instead of "double" in the "shorter formula" above, even though the following bullet points make it clear I'm talking about doubling. Fixed now.