The following series follows a certain pattern, Find which of the following statement is correct.

20, (a), (b), (c), 80

a - b = (x + 1)2 - y

a + b = (y - 4)2 - 8x

c + a - b = (y - 2x - 3)2 - (x + 2)2

x = H.C.F of two consecutive odd numbers

y = L.C.M of three consecutive smallest positive even numbers.