Today is a special day for those with an affinity for numbers.
Today April 4, 2016 (4/4/16) is (unofficial) Square Root Day.
The name was coined by a Californian mathematician called Ron Gordon.
He had his 'Eureka' moment when he was writing down the date September 9, 1981 and noticed that there was an interesting feature about the numbers in it - 9/9/81.
81 was the product of 9 squared, 9 was the square root of 81.
Dates such as these are pretty rare. In fact, Gordon observed that there are only nine dates in every century which share similar attributes - 2/2/4, 3/3/9, 6/6/36, 7/7/49, 8/8/64 and 9/9/81.
The previous Square Root Day was celebrated on March 3, 2009 and the next one will occur on May 5, 2025.
"Square Root Days are special because they're so rare," says Gordon.
"We only get a handful of them in a century. They're like calendar comets. You wait and wait and wait for them, they brighten up your day and then - poof! They're gone."
Gordon has plenty of interesting tidbits to help celebrate the day, including the fact the US president Barack Obama is the country's first square root president.
"We have Obama, the 44th president, governing in 2016. He is the first and probably the only square root president, he said.
Gordon also introduced two other mathematical holidays - Odd Day (11/13/15) and Trumpet Day (2/2/22 - read it aloud and you'll notice the sound it makes, 'two-two-two-two', is similar to a trumpet noise).
According to Gordon, Square Root Day is "a good day to.......get things squared away, try to fit a square peg into a round hole, go square dancing, tie a square knot, travel on Route 66, drink rootbeer from a square glass, root for the underdog, eat a square meal, or watch the pigs root around."
He's even invented a competition for creative people to win the date in cash (€441.6) which is divided between 4+4+4+16 winners.
The prize is open to Irish audiences. To enter, contestants must come up with an inventive way to celebrate the day. Entries must be completed within 4+4+16 days of Square Root Day and submitted, by email (firstname.lastname@example.org) or by post (Box 5133, Redwood, California, 94063).