Rare 1943 copper coin fetches a pretty penny in auction. This is how rare it is.

According to the American Numismatic Association, the 1943 copper–alloy cent is one of the most idealized and potentially one of the most sought–after items in American numismatics. Nearly all circulating pennies at that time were struck in zinc–coated steel because copper and nickel were needed for the Allied war effort.

Approximately 40 1943 copper–alloy cents are known to remain in existence. Coin experts speculate that they were struck by accident when copper–alloy 1–cent blanks remained in the press hopper when production began on the new steel pennies.

Don Lutes Jr. kept the 1943 copper penny he stumbled upon in his high school cafeteria seven decades ago in a safe behind a wall in his Massachusetts home.

All US pennies were supposed to be made of zinc-coated steel that year to conserve the copper needed for wartime essentials like shell casings and telephone wire, according to Heritage Auctions, a Dallas-based auction house. But a small number of copper pennies were created by mistake. Only a few of them exist today, making them special to coin collectors.

Lutes knew his coin was rare and held on to it. But as his health declined last year, Lutes decided to sell the coin because," he wanted to make sure it went to a good home," said Peter Karpenski, a friend and fellow coin collector.

Lutes' prized possession fetched a pretty penny -- $204,000 -- after a live auction Thursday at the Florida United Numismatics convention in Orlando, Florida. Heritage Auctions, which oversaw the sale, estimated the coin was worth at least $170,000.

The top bid after a two-week online auction had been $130,000, according to Heritage Auctions

"What makes this so exciting is that it's the only time ever in history when the discovery coin for this piece has been available for sale. In other words, this was the first one that was ever found," said Sarah Miller, Director of Numismatics for Heritage Auctions' New York office.

A 1943 copper cent was first offered for sale in 1958, bringing more than $40,000. A subsequent piece sold for $10,000 at an ANA convention in 1981. The highest amount paid for a 1943 copper cent was $82,500 in 1996.

Because of its collector value, the 1943 copper cent has been counterfeited by coating steel cents with copper or by altering the dates of 1945, 1948, and 1949 pennies.

The easiest way to determine if a 1943 cent is made of steel, and not copper, is to use a magnet. If it sticks to the magnet, it is not copper. If it does not stick, the coin might be of copper and should be authenticated by an expert