It's probably a common error called a filled die, in which case it has no extra value.
Cents are struck in huge numbers at high speed and are subject to many minor minting problems. Sometimes a bit of crud gets into the little recesses that form the letters or numbers, and prevents the metal from flowing cleanly. After a few cycles the crud falls out and everything's fine again.
it was made in denver, at the denver mint
denver
The 1957 D Wheat Penny was made in Denver Colorado. The "D" is the mint mark for the Denver mint.
The D on a penny indicates it was made at the Denver, Colorado mint
It was struck at the US Mint at Denver Colorado - D for Denver.
Yes the D is the mint mark for Denver on the penny.
A 1999 Denver Mint penny is not worth appreciably more than other pennies. In most collections, this penny would only be worth one cent.
The letter on a penny refers to the mint at which it was manufactured. P is Philadelphia, D is Denver.
Denver, Colorado.
3 cents.
100.000.000
"D" on a steel penny typically refers to the Denver Mint, where the penny was minted. During World War II, steel pennies were produced due to a copper shortage.