Maybe I'm looking at this the wrong way, but I'd handle enumerating this just like enumerating a set of three numbers. For an integer i just do (1-2(i%2)) * (i/

Maybe I'm looking at this the wrong way, but I'd handle enumerating this just like enumerating a set of three numbers. For an integer i just do (1-2(i%2)) * (i/2) using integer division. If it's recursively enumerable with natural numbers then it has to be trivially extendable to all integers just by that method alone.