Binary Days

According to the all-knowing Twitter-verse, yesterday (10 October 2010) was binary day. If you ignore the “20” part of “2010”, the numerical date (10-10-10) is a binary number. In fact, it is the binary representation of the decimal number 42, which some nerds find particularly relevant for some reason[1].

While we are getting really excited about coincidence, today is also a binary date (11 October 2010 = 57). Not that binary dates are that rare in the beginning of any particular century. Using the “no year 0” definition of the 21st Century[2], there will be 36 binary dates (and using the sensible day-month-year notation[3]):

1 January 2001/2010/2011/3000 = 21/22/23/20
10 January 2001/2010/2011/3000 = 37/38/39/36
11 January 2001/2010/2011/3000 = 53/54/55/52
1 October 2001/2010/2011/3000 = 25/26/27/24
10 October 2001/2010/2011/3000 = 41/42/43/40
11 October 2001/2010/2011/3000 = 57/58/59/56
1 November 2001/2010/2011/3000 = 29/30/31/28
10 November 2001/2010/2011/3000 = 45/46/47/44
11 November 2001/2010/2011/3000 = 61/62/63/60[4]
*For dates that correspond to prime numbers, I have highlighted the year in bold.

Of course, real binary dates like, 11 November 1111[5] (255 in decimal numbers), will not be seen again for about another 8000 years, during which time we are virtually certain to change the calendar, again.


  1. I wonder how Douglas Adams would feel about the meaning that his meaningless, inscrutable, random number has taken on due to his writings. He’d probably laugh.
  2. Yes, I’m sticking to the there is no year 0 argument.
  3. If you disapprove of this hierarchically sensible arrangement, but are “geeking-out” over binary, you need to get your logic house in order.
  4. Armistice/Veterans/Remebrance Day, commemorating the end of WWI
  5. The most recent real binary date.

Author: Josh Witten

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