41, 44, 47, 49
that's 4 total, enough powers to take every patron power.
Note that you get three enhancement slots at every level you don't get a power. This means you cannot fully slot both your lvl 47 and your level 49 power - you only get slots for these at 48 and 50, six slots total (plus the "free" slot in each power".
How many more powers do we get from L40-50 please?