Quick! What is the next term in the numerical sequence 1, 2, 1, 2, 3, 4, 5, 4, 3, 4, ...? If you said '3', then you must be an American history expert, because that sequence represents the number of living US presidents beginning with Washington's inauguration on 30APR1789 and continuing until the death of James Monroe on 04JUL1831.

I stumbled upon the Wikipedia page for "Living Presidents of the United States," which contains a table that shows the dates of inaugurations and deaths of US presidents and the number of living presidents between events. The table is very crowded and I found it difficult to visualize the data, so I decided to create a SAS graph that shows the timeline for the number of living US presidents.

All the information in the complex Wikipedia table can be derived by knowing the dates on which a new president was inaugurated or a previous president died. You can create a simple data set with that information and use SAS to calculate other information, such as the number of living presidents or the time span between events. You can download the data and the SAS program that creates the following graph. (Click to enlarge.) If you create the graph in SAS, you can hover the mouse over a marker to see which president died or was inaugurated for each event.

A few interesting facts that are revealed by the visualization of these events (all statistics as of 08MAY2017):

• The time-weighted average since Washington's inauguration is 3.43 living presidents per day.
• The period from 1989 to 2017 featured a larger-than-usual number of living presidents. Unfortunately, I don't expect that trend to last, since Presidents Carter and G. H. W. Bush are both very old.
• There have been six brief intervals when the only living president was the sitting president.
• On 04JUL1826, the US lost two former presidents (John Adams and Thomas Jefferson) within 6 hours. You can see the graph drop by 2 in 1826. Interestingly, James Monroe also died on Independence Day!
• When a president dies in office, the number of living presidents does not change, since the vice-president is inaugurated that same day. Can you spot the eight times that a president died in office?
• No presidents died during F. D. Roosevelt's administration—except FDR himself. The 20-year period from 1933-1953 is the longest span during which the number of living presidents stayed constant.
• The reason no one died during FDR's terms was that Herbert Hoover remained alive. Hoover had the record of being the ex-president who lived longest after his inauguration: from 1929 until 1964, which is 13,014 days or 35.65 years! However, Jimmy Carter broke that record a few years ago. Carter was inaugurated in 1977 and has lived more than 40 years since that event.

Do you notice any other interesting features of this timeline? Leave a comment.