Figuring that the mana cost you calculate there is mana-per-frame, I took a look at the resulting mana-per-second costs for a couple skill levels.
1: 25 * (35 + 1) / 64 = 14.0625
5: 25 * (35 + 5) / 64 = 15.625
6: 25 * (35 + 6) / 64 = 16.015625
What caught my eye is that if you halve these values (and then round down in order to take into account lying-character-screen), they are consistant with the (admittedly few) data points Vash provides above. Slvls 1-5 show 7 mana per second, and slvl 6 displays 8. I have no idea at all why this might work this way; my only theory is that Inferno casts every second frame. More data is needed to confirm, and someone more well-versed in the game's inner workings is needed to explain.
Assuming that this is the way it works, inferno's mana cost will display as 8 for lvls 6-11, 9 for 12-16, 10 for 17-21, and 11 for 22-26, while actually costing very slightly more mana.
EDIT: Also, I'm fairly sure that the 'repeat' column means to continue casting without restarting the cast animation if the button is held down; that seems to be the common factor of the three listed skills. I don't think this impacts mana cost calculations.
1: 25 * (35 + 1) / 64 = 14.0625
5: 25 * (35 + 5) / 64 = 15.625
6: 25 * (35 + 6) / 64 = 16.015625
What caught my eye is that if you halve these values (and then round down in order to take into account lying-character-screen), they are consistant with the (admittedly few) data points Vash provides above. Slvls 1-5 show 7 mana per second, and slvl 6 displays 8. I have no idea at all why this might work this way; my only theory is that Inferno casts every second frame. More data is needed to confirm, and someone more well-versed in the game's inner workings is needed to explain.
Assuming that this is the way it works, inferno's mana cost will display as 8 for lvls 6-11, 9 for 12-16, 10 for 17-21, and 11 for 22-26, while actually costing very slightly more mana.
EDIT: Also, I'm fairly sure that the 'repeat' column means to continue casting without restarting the cast animation if the button is held down; that seems to be the common factor of the three listed skills. I don't think this impacts mana cost calculations.