The Sensex at the Bombay Stock Exchange surged 257 points, or 1.2 percent, to close at 21,289, on Wednesday, on good buying by investors after wholesale inflation cooled to a five-month low, and as global markets gained ground. The Nifty at the National Stock Exchange rose 79 points, or 1.3 percent, to 6,321.Stock markets in Japan, Hong Kong, South Korea and Singapore rose between 0.4 percent and 2.5 percent.