In this case, a rare penny, expected to fetch about $170,000 at auction this week, brought in a little over $200,000.

The 1943 copper penny was minted in Philadelphia and is one of an estimated 10 to 15 in existence. Heritage Auctions spokesman Eric Bradley tells Fortune that the coins are rare because they weren’t made of zinc-coated steel, as were others at the time.

The princely sum—officially $204,000—wasn’t the highest price paid for an historic penny. Another World War II-vintage copper penny, the only known penny mistakenly cast in bronze at the Denver Mint, sold in 2010 for $1.7 million, owing to its rarity.

Nor is it the highest price paid for an American coin: A century-old nickel sold last year for $4.5 million, and three years ago, an especially rare dime sold for $2 million.

Tom Caldwell, of Concord, Mass. was the top bidder of the Philadelphia penny. He says he plans to display it at various coin shows around the country. The money raised from the sale will go to the Pittsfield Public Library, where Don Lutes, Jr., the original owner of the coin, was a patron until his death last September.

Lutes received the penny in 1947 as change for his school lunch. Intrigued, he asked the U.S. Treasury if it had made any copper pennies in 1943 and was told no. He kept the coin anyway.

In the following years, he learned there were, in fact, copper pennies mistakenly made that year when the U.S. Mint was supposed to be saving copper for the war effort. By 1958, a similar penny sold for $40,000, the equivalent of more than $350,000 today.

Correction, January 11, 2018: The original version of this article, including the headline, overstated the auction estimate for the coin. We regret the error.