what american penny is worth money?
Cent
contradiction
 = = = Dollar and $ 50 pieces = = = 

contradiction
 Where the hundreds of millions of them went remains somewhat of a mystery today . In the meantime , Washington quarters , the same design used since 1932 , became the highest value coin of the realm , in terms of circulation use . These were particularly popular for vending machines , arcade games , and the like . Today , this continues to be the case , and Kennedy half dollars as well as the later mini @-@ dollar coins , are almost never encountered . " 

neutral
 Despite their unpopularity in the United States , the coins proved popular for commerce in El Salvador and Ecuador , nations that use the United States dollar . 

entailment
 The American twenty @-@ cent piece is a coin struck from 1875 to 1878 , but only for collectors in the final two years . Proposed by Nevada Senator John P. Jones , it proved a failure due to confusion with the quarter , to which it was close in both size and value . 

neutral
 All of these $ 50 pieces , public or private , are very rare and valuable today : One of Humbert 's octagonal pieces , dated 1851 and with a lettered edge , sold at auction in 2010 for $ 546 @,@ 250 . The only $ 50 piece produced by the United States Bureau of the Mint prior to 1915 was the 1877 pattern half union , produced experimentally at the Philadelphia Mint , though it was not approved as a circulating coin . 
