That's the total number of military veterans in the United States as of 2011, according to the U.S. Census Bureau, in a fact sheet aboutVeterans Day 2012, which contains many other interesting statistics about Those Who Served.
Of the 21.5 million U.S. veterans, 1.6 million are women.
9.2 million are older than 65; 1.8 million are younger than 35.
3.5 million veterans have a service-connected disability rating.
That's the percentage of noncombat firearm-related deaths between 2002 and 2011 identified as suicides, among servicemembers ages 30 and older, according to data in the September issue of the Armed Forces Health Surveillance Center's Medical Surveillance Monthly Report.
The number of beneficiaries, worldwide, that are served by the military health care system, according to a new report from the Congressional Research Service, Military Medical Care: Questions and Answers (PDF).
The percentage of children in Department of Defense K-12 schools worldwide who received special education services in the school year 2011-2012, according to a recent Government Accountability Office (GAO) Report -- Military Dependents: Better Oversight Needed to Improve Services for Children with Special Needs.