c = (2^40 + 2^39 + 2^38) : 7 =
2^38 x (2^2 + 2 + 1) : 7 =
2^38 x 7 : 7 =
2^38 =
(2^19)^2 = > patrat perfect
d = (4^50 + 4^49 + 4^48) : 21 =
4^48 x (4^2 + 4 + 1) : 21 =
4^48 x 21 : 21 =
4^48 = (4^24)^2 = > patrat perfect
4^48 = (4^16)^3 = > cub perfect
