There are ways to get in trouble with the law for just about everything: smoking weed, theft, horse theft, stealing a horse and teaching it to smoke weed, and even shouting "fire" in a crowded not-on-fire stable full of stoned horses. But numbers are pure and theoretical and definitely exempt from legal action, right?
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Wrong, buddo. And the reason is that in the digital age, huge prime numbers are really, really important for encryption. So important, in fact, that having or sharing some of them could get you prosecuted under the Digital Millennium Copyright Act, which prohibits people from subverting copyright-prevention measures.
Back when people still bought DVDs, those discs were encrypted with a content scrambling system to keep people from ripping and burning them. Software to copy DVDs started circulating soon after the DMCA passed, and movie studios sued those distributing the software not long after that. It was Phil Carmody who discovered a 1,401-digit prime number -- no, we're not going to post it -- that made the wholesale copying of DVDs possible. And the Motion Picture Association of America argued that mere possession of this number could still be considered an attempt to circumvent copyright. Weren't the early days of piracy exciting?
Keep in mind these lawsuits were happening in 1999 and 2000, back when Kazaa was a new threat and big companies still thought it behooved them to make examples out of individual pirates. The odds of being prosecuted in 2016 for possession of a very big, mostly indivisible number is near zero. Even still, the MPAA won its cases largely because of the judge's decision that code did not constitute protected speech -- it's an issue that remains unresolved and recently cropped up again when the FBI started demanding backdoors to locked Apple products. Seek out this number at your own risk.