Happy Square Root Day

For those of you who have been living in a cave, today is Square Root Day. Square Root Day is an unofficial holiday where the month and day are the square root of the last two numbers of the year.

Today is 3/3/09. You see how 3 is the square root of 9? There are only nine such days in any given 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

A couple of exceptions occur each millennium as well. There is 10/10/2100, 11/11/2121, 12/12/2144.

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

2k + 1 = (k + 1)² – k².

The ‘generally accepted’ method of celebrating Square Root Day is to cut a radish or other root vegetable into squares to eat, thus creating ‘square roots’.

Hah! I bet you weren’t expecting a math lesson, were you?