Basically, he suggested that he'd walk in on day one of his administration and order a firing of fed workers....based on your social security numbering in a even-number or a odd-number.
Legal? Yeah, in fact, you'd bypass years of challenges in court....by this method. You'd just get a notice at 8 AM....clear your desk, and here's some exit check.
Now, you might ask....what if there are more 'odds' than 'evens' in the government service sector? Well....no one has ever collected such data....so you might be correct.
The odds that more 'evens' are incompetent, than 'odds'? Maybe, but it might be chance to energize incompetent folks.
More incompetent managers who are 'evens'? That's a possibility.
I suspect his idea is to target one single agency (DoJ for example), and use this as a 'test'.