There are twice as many unique 18-digit combinations as seconds since the Big Bang. Generate a number at random, say it out loud, and claim your number. You will forever be the first person to say the number. A tiny act of ownership in an infinite space.
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Congratulations! You are (highly-likely) to be the first person to ever say this number out loud, and you may be the only person to ever say it forever. It is your number. Proudly go around uttering it, share it with friends, print it on a t-shirt, or whatever else you may fancy.