Yes, I did the math. Wish I still had the spreadsheet.
It's not as simple as multiplying the population. The point is that if everyone gets that check, then you can raise the nominal tax rate much higher but still get the effective tax rate (i.e. income - tax + UBI) in reasonable territory. As I recall I actually went all in and also made it a flat income tax to see how much the UBI offset would work at making it effectively progressive, and that also works out.
It's not as simple as multiplying the population. The point is that if everyone gets that check, then you can raise the nominal tax rate much higher but still get the effective tax rate (i.e. income - tax + UBI) in reasonable territory. As I recall I actually went all in and also made it a flat income tax to see how much the UBI offset would work at making it effectively progressive, and that also works out.