The Nikkei stock index fell for a third consecutive day on Thursday, hitting a three-week low due to sharp declines in technology shares, while investors remained cautious ahead of a slew of U.S. economic data set for release later in the day. The 225-issue Nikkei Stock Average ended down 390.52 points, or 1.05 percent, from Wednesday at 36,657.09, its lowest level since Aug. 14. The broader Topix index finished 12.73 points, or 0.48 percent, lower at 2,620.76. On the top-tier Prime Market, decliners were led by insurance, pharmaceutical and retail issues. The U.S. dollar fell to the lower 143…