Find the next number in the given number series? 50, 51, 47, 56, 40, ?

The given number series is 50, 51, 47, 56, 40, ?

$5050 + 12 = 5151 - 22 = 4747 + 32 = 5656 - 42 = 4040 + 52 = 65$

Hence, the next number in the given number series is 65.