Big week for serial robbery! We’ve got gun robbers, a mace robber, livery cab robbers, and now a knife robber — and a busy one, so look out, Upper East Siders. He’s armed with “what is described as a long kitchen knife,” says NYPD. On September 4th at 12:45 a.m., he struck at York Avenue and East 80th Street. A little after 10 p.m. that night, he seems to have pushed into an apartment building at York Avenue and East 83th Street, and cut his victim on the leg when he resisted. Tuesday night he knife-robbed someone at Second Avenue and East 75th Street, and in the wee hours of Wednesday he robbed two guys at Third Avenue and East 80th Street. The suspect is described as a black man between 35 and 40 years of age and between 5’10” and 6’0″, with close cut hair and a mustache. In one of the incidents he wore an orange safety vest. If you have information as to these men or this incident, NYPD asks you to contact 1-800-577-TIPS(8477), www.nypdcrimestoppers.com, or text 274637 (CRIMES), then enter TIP577.