It's in the 21% - 22% range (55 million (SS) of what is outside the 200 million referred to as Adult 15 - 65.) Perhaps 47% is including infants and up, out of 311 million total.
Actually, It comes from the Joint committee on Taxation. It is 51% of ALL households. Not people. 31% actually received more money than paid in. So your figure is wrong in reality.