Rising for the sixth straight session, the Sensex at the Bombay Stock Exchange gained 157 points, or 0.9 percent, to close at an 11-week high 17,234 on Friday, on sustained buying by investors, on easing food inflation.The Nifty at the National Stock Exchange rose 46 points, or 0.9 percent, to 5,205.Stock markets in Hong Kong , South Korea and Singapore rose between 0.3 percent and 0.8 percent.