If you ask someone familiar with American history to rank by frequency of references in the Americana Exchange Database the last names of the Presidents you create an interesting challenge.  Many, even most, are important and if importance is the crucial factor we can all write up a list beginning with most important at the top.  If there are other factors, and there are, the list will be a bit more complicated to correctly sequence.

Here are some of those factors.  Of the 44 US Presidents six have the same last name so our list of Presidential last names will be 38 rather than 44 and six of them will have a double weight.  They are: 
 

Adams

Harrison

Johnson

Cleveland

Roosevelt

Bush

Years of exposure are also important.  Obama recently had 419 references, the lowest number of any President.  He’s also the newest President.  If the number of references is exclusively a function of elapsed time then the older Presidential last names will always have the most references.  This however is not the case.
 

Importance is another factor. There is a small group of ultra-important Presidents – Washington, Jefferson, Jackson, Lincoln and the Roosevelts whose material excites more interest in the auction rooms and more admiration among historians. This too needs to be factored in.