Groupon Inc.’s decision to push ahead with an initial public offering as other start-ups hold off may be driven more by necessity than choice: The company needs cash to keep growing and is nearing the number of shareholders that requires it to report financial results, Bloomberg reported. Groupon is seeking to raise as much as $540 million, saying it won’t need to use the money for at least a year and has no urgent cash needs. Even so, the biggest provider of online daily deals owed almost twice as much to merchants at the end of September as it held in cash. Marketing costs rose 37 percent in the latest quarter, four times as quickly as its cash pile, Bloomberg said.