At the risk of ruining a joke, the sum of all numbers representable by a signed n-bit integer using 2's complement is -2^(n-1). -2^(n-1) is the only negative n

At the risk of ruining a joke, the sum of all numbers representable by a signed n-bit integer using 2's complement is -2^(n-1). -2^(n-1) is the only negative number that does not have a positive counterpart in this representation.