Clicky.

"In hidden vaults across the country, the US government is building a stockpile of $1 coins. The hoard has topped $1.1bn, and the piles have grown so large the US Federal Reserve is running out of storage space... Yet the piles have continued to grow because the law requires the US Mint to issue four new presidential coins each year even if most of the previous year's coins remain in government vaults."
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