NEW YORK — Nora Roberts is so prolific she had to take up a pen name so her publisher could release more books by her each year. “I’m a fast writer,” Roberts told The Associated Press in a rare interview. She typically releases four books a year, and has for more than four decades. It’s not just about her speed. It’s her range, too. She’s written more than 250 books, from romantic one-offs and fantasy-themed trilogies to a police procedural series she’s been writing for three decades.