RemoveUndefined Command

RemoveUndefined( <List> ): Removes undefined objects from a list.

RemoveUndefined(Sequence((-1)^i, i, -3, -1, 0.5)) removes the second and fourth element of the sequence since expressions \((-1)^\{1.5}\) and \((-1)^\{2.5}\) are undefined and yields list \{-1, 1, -1}.