The US issued a 15-cent BANKNOTE in the 1870s. It's a complete non-sequitir. It was part of a sort of emergency issue meant to replace the silver coins that d

The US issued a 15-cent BANKNOTE in the 1870s. It's a complete non-sequitir. It was part of a sort of emergency issue meant to replace the silver coins that disappeared during the Civil War and weren't returned fast enough, but there was no 15c coin to replace. More relevant to this community, it always made me think about the abstract math of change making algorithms. With the coin denominations we have in the US, the optimal (fewest number of coins) change can always be made by going for the largest coin available less than the remaining balance due. It's entirely possible to make a currency system that was not the case. As a trivial example: In a hypothetical system with coins denominated 20, 15, 10, 3, 2, and 1 (basically the Soviet-era model without the 5-kopeck coin) the optimal way to make 25 units (15+10) is not the "largest first" way (20+3+2)