A convicted child rapist moved into an apartment building directly across from a Bronx school — sneaking past any neighbors who signed up for sex-offender alerts, The Post has learned.

Arthur Ceasar, who repeatedly raped and sodomized a 15-year-old girl in 1993, gave authorities the wrong ZIP code for his new home at 1965 Lafayette Ave., directly opposite the Adlai Stevenson Educational Campus.

Nearly 2,500 students attend six high schools and a combined middle/high school in the massive, four-story building.

In a stunning legal loophole, state law bars sexual predators from living within 1,000 feet of schools only if they are on parole or probation.

Ceasar, 50, was sprung from prison in 2001 after serving two thirds of a six- to 12-year sentence, but he got sent back twice on parole violations before maxing out his sentence in 2005, records show.

The ZIP for both the school and his apartment building is 10473, but Ceasar told the state Department of Criminal Justice Services he was living in 10469, about five miles north of there.

The inaccurate information was uncovered by state Sen. Jeff Klein (D-Bronx), whose office was notified about his new address Wednesday by the NY-Alert system.

In addition to other notifications, NY-Alert informs users when a serious sex offender moves in or out of their area.

Klein’s office informed the NYPD, which busted Ceasar on Thursday for missing a Feb. 22 deadline to keep authorities up to date on his whereabouts.

Ceasar was charged with two felonies for failing to verify his address. He was sent to The Tombs jail in lower Manhattan on $1,500 bail or $3,000 bond, records show.

His rap sheet lists 31 prior arrests, cops said, including the bust that led to his conviction for first-degree rape and an open case for pot possession.

Ceasar is listed as a Level 3 sex offender — the worst possible — meaning he poses a “high risk of repeat offense and a threat to public safety.”

Neighbors were furious.

“I’m really shocked. I had no idea this guy was right down the hall from me,” said Linda Tyler, 62.

“How is it I wasn’t made aware of this? I have a daughter who just came home from school who just turned 26. I’m going to have to tell her to watch herself.”

A neighbor at his prior Bronx address — a block from the East Fordham Academy for the Arts middle school — said she was “happy he doesn’t live here anymore.”

“As a female, I never felt safe around him,” said Jessica Pimentel, 20.

“My mom told me once that he was a rapist, so after that, I would never have a conversation with him,” she recalled.

“I would step to the side and let him pass. There was just something about him. He just gave off a look I didn’t like.”

Additional reporting by Daniel Prendergast