R. Kelly needs to be locked up for more than a quarter century … according to federal prosecutors, and that’s just for the one case for which he’s been convicted.

Federal prosecutors out of the Eastern District of NY — who won a conviction against Kelly last September — just filed their recommendation for his sentencing, and they believe there’s more than enough reason to send him away for "in excess of 25 years."

In the docs, obtained by TMZ, the feds say Kelly’s particularly menacing because of his history of enticing minors. Prosecutors hold up the case of his relationship with Aaliyah as a prime example, saying he "began to sexually abuse her when she was just 12 or 13 years old." As they laid out in the trial, Kelly went on to marry her in an attempt to cover up that abuse and dodge criminal charges.

Other reasons prosecutors want the judge to throw the book at Kelly include his recordings of child pornography … and the "physical and psychological" abuse of women. Of course, much of that was detailed in the "Surviving R. Kelly" documentary — things like Kelly making women call him "Daddy," violent spankings if they disobeyed his rules, and prolonged isolation as punishment.