Square Root Day is an unofficial holiday celebrated on days when both the day of the month and the month are the square root

Square root

In mathematics, a square root of a number x is a number r such that r2 = x, or, in other words, a number r whose square is x...

 of the last two digit

Numerical digit

A digit is a symbol used in combinations to represent numbers in positional numeral systems. The name "digit" comes from the fact that the 10 digits of the hands correspond to the 10 symbols of the common base 10 number system, i.e...

s of the year. For example, the last Square Root Day was March 3, 2009 (3/3/09), and the next Square Root Day will be April 4, 2016 (4/4/16). The final Square Root Day of the century will occur on September 9, 2081. Square Root Days fall upon the same nine dates each century.

Ron Gordon, a Redwood City, California

Redwood City, California

Redwood City is a California charter city located on the San Francisco Peninsula in Northern California, approximately 27 miles south of San Francisco, and 24 miles north of San Jose. Redwood City's history spans from its earliest inhabitation by the Ohlone people, to its tradition as a port for...

 high school teacher, created the first Square Root Day for September 9, 1981 (9/9/81). Gordon remains the holiday's publicist

Publicist

A publicist is a person whose job is to generate and manage publicity for a public figure, especially a celebrity, a business, or for a work such as a book, film or album...

, sending news release

News release

A press release, news release, media release, press statement or video release is a written or recorded communication directed at members of the news media for the purpose of announcing something ostensibly newsworthy...

s to world media

News media

The news media are those elements of the mass media that focus on delivering news to the general public or a target public.These include print media , broadcast news , and more recently the Internet .-Etymology:A medium is a carrier of something...

 outlets. Gordon's daughter set up a Facebook

Facebook

Facebook is a social networking service and website launched in February 2004, operated and privately owned by Facebook, Inc. , Facebook has more than 800 million active users. Users must register before using the site, after which they may create a personal profile, add other users as...

 group where people can share how they were celebrating the day.

One suggested way of celebrating the holiday is by eating square

Square (geometry)

In geometry, a square is a regular quadrilateral. This means that it has four equal sides and four equal angles...

 radish

Radish

The radish is an edible root vegetable of the Brassicaceae family that was domesticated in Europe, in pre-Roman times. They are grown and consumed throughout the world. Radishes have numerous varieties, varying in size, color and duration of required cultivation time...

es, or other root vegetable

Root vegetable

Root vegetables are plant roots used as vegetables. Here "root" means any underground part of a plant.Root vegetables are generally storage organs, enlarged to store energy in the form of carbohydrates. They differ in the concentration and the balance between sugars, starches, and other types of...

s cut into shapes with square cross section

Cross section (geometry)

In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...

s (thus creating a "square root").

Full list of Square Root Days

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

Distribution of Square Root Days

The number of years between consecutive Square Root Days in a century are consecutive odd numbers: 3, 5, 7, 9, 11, 13, 15, 17. This illustrates the fact that every odd number is the difference of two consecutive squares.