According to Wikipedia, Square Root Day is an unofficial holiday celebrated on days when both the day of the month and the month are the square root of the last two digits of the year. 

It only occurs 9 times every century.  Next one won’t be until 4/4/2016. 

Square Root Day occurs on the following dates each century:

• 1/1/01
• 2/2/04
• 3/3/09
• 4/4/16
• 5/5/25
• 6/6/36
• 7/7/49
• 8/8/64
• 9/9/81