A mnemonic based on every 5th item to be remembered, using one's fingers as a kind of abacus. You put up one finger for each one as you go along. When you reach the fifth finger, that becomes the first letter of the mnemonic. This device works well when the number of entities to be recalled is too large for conventional mnemonics to easily accommodate.
Example: Nlnci Sjgai is one possible pentamnemonic for all the countries with some coastline on the continent of Eurasia. If you start with the western-most point-Portugal-and go clockwise around the coast, your first 'bookmark country' is Netherlands, and you end with Italy. (Just add on Monaco, the 51st country) Portugal, Spain, France, Belgium, NETHERLANDS: Germany, Denmark, Poland, Estonia, LITHUANIA. When your little finger gets extended, you must always arrive on a country that begins with one of the consecutive letters in Nlnci Sjgai, or you forgot a country.
A mnemonic system based on every 5th item to be recalled. It is quite useful for alert young minds, but can be misused by those in their dotage.
Surprised nobody caught this, but the example for pentamnemonic above explains my concern about seniors employing this technique. If your mouse requires a walker, you might make the same mistake and get it wrong.
I forgot Kaliningrad in the original example, which is a disconnected part of Russia, and inserted Estonia in it's place. Estonia is actually north of Latvia, which borders Lithuania. Its a small planet, and 70% is water. With only 193 countries there's no excuse for misplacing them. Sorry.