In Business This Week
-- Toys 'R' Us will buy back up to $1 billion of its stock, and open 115 stores in 1994.
-- Four months after losing Absolut vodka, Grand Met will sell Stolichnaya instead.
-- RiteAid said it will sell off four noncore businesses and close 200 drugstores.
-- Cray Research computed the largest prime number known, with 258,716 digits.EDITED BY KEITH H. HAMMONDS