11 is the Aliquot sum of one number, the discrete semiprime 21 and is the base of the 11-aliquot tree.
As 11 is the smallest factor of the first 11 terms of the Euclid–Mullin sequence, it is the 12th term.
An 11-sided polygon is called a hendecagon or undecagon.
In both base 6 and base 8, the smallest prime with a composite sum of digits is 11.
11 is an Eisenstein prime with no imaginary part and real part of the form 3n − 1.
Displayed on a calculator, 11 is a strobogrammatic prime and a dihedral prime because it reads the same whether the calculator is turned upside down or reflected on a mirror, or both.
I have no idea what most of that means, but I was thinking about eleven as I painfully completed my taxes over the weekend as well as inputting FASFA (those of you with kids in college know what I mean) data for my now two college age children. In whole, the process left me feeling like I had just gotten a protological exam from Andre the Giant.
"Spread 'em and you had better smile, mon ami!"
In short, I needed a diversion so naturally I starting thinking about baseball and equally naturally, I started thinking about the NFBC. We have a lot of new members and as we go down to the wire for people signing up (including ones who might feel burned by another unfortunate failure), I thought I would share what got me to the NFBC...eleven years ago...in 2004.
In early 2004, a friend and co-worker and I were discussing baseball while I was at Nortel (another collapse). Jay was his name and he was one of the insidious NY Mutt fans (man, you just can't get away from those guys). I was ya-yaing him because Glavine, who left the Braves in 2003 in a fit of confusion to play for the Mets, was coming off a horrible year and I was predicting a further decline from which Glavine would never recover (see, I was lousy at this even then). I was also extolling how I was going to dominate (proof of my obvious intelligence) my local fantasy baseball league again. Jay was reading some publication that had an ad about this National Fantasy Baseball Championship. Brand new. Unproven. High stakes and damned expensive compared to the $100 leagues I was used to. Basically, I was goaded into putting up or shutting up. I went home and firmly told my wife "I am going to Vegas to play high stakes fantasy baseball and I do not want any guff about it!" Actually, I think the conversation started "Honey, are you asleep?" but in any regard I ended up in Vegas for the second time in my life. And I was going to show how it was done, by God...and I ended up in a league with Childs and Rey Diaz and Gene McCaffery...with predictable results.
All of that to say this...to any who are on the fence...I have not regretted one year...Vegas, Chicago, Florida...all fun, all worth it, and even though 2004 was a bath for Greg and Tom and Krause, everyone was treated well and paid what they were do. Same results though now we have a third company in charge. Same Greg. Same Tom. Same great contest. Some have left for whatever reason, some were mad when they did it, though I think those guys mainly had the problem of a supersized stick in their keister.
I am back this year and I still look forward to it. How many others have done the Main Event for eleven straight years?
1. Wayne "Still don't like the Mets" Edwards
11 years for me. 5th yr in row for Vegas I believe. 
Just one of the many great people and great friends that I've made being a part of the NFBC. Looking forward to seeing you in Vegas. 