Which letter will replace the question mark (?) in the following series?

L8, N9, P64, R25, ?

T216

According to the above alphabet position:

L8    ⇒ (12), 2³

N9     ⇒ (14), 3²

P64   ⇒ (16), 4³

R25   ⇒ (18), 5²

?       ⇒ (20), 6³ = T216

(add 2 in 1st alphabet position and there is cube and square of consecutive numbers respectively in 2nd alphabet position)