Here the given number series is 5 11 21 44 ? 175
Now the given series follows a pattern, that
x2 + 1, x2 - 1, x2 + 2, x2 - 2, x2 + 3, x2 - 3,...
Then the missing number is x2 - 2
= 44 x 2 - 2 = 88 - 2 = 86
Hence, the missing number in the number series is 86.
