Franchise: Halo

There has been a long-standing tradition by Bungie and 343 Industries to insert references to the number 7 into the Halo series. This phenomenon of trying to figure out what is and is not a reference to the number 7 is similar to the 23 enigma, a numerological belief coined by author William S. Burroughs about finding connections to prove the significance of the number 23 in real-life. The name of the dedicated Halo studio 343 Industries, and its namesake 343 Guilty Spark, are just two examples of the number 7's prominence in the series, as 343 can be derived from 7 in a few different ways:

7x7=49
49x7=343

7x7x7=343

3+4+3=10
10-3=7

Larry Niven (author of the Ringworld series of books) was once approached by Del Rey Books to write a Halo novel, but turned them down due to his lack of familiarity. Microsoft had even sent him an Xbox and a copy of Halo: Combat Evolved (among other games) to try to convince him.

There was a Halo game partially developed for the Nintendo DS, but it was ultimately canceled. The game had been developed to a point of being playable.

After Apple and Google created their own Intelligent Personal Assistant, "Siri" and "Google Now", Microsoft made their own system under the name Cortana, based on the Artificial Intelligence character from the Halo series. Cortana's voice actress, Jen Taylor, returns to voice the system, too.

During the development of Halo 3 and Halo Wars, Microsoft gave the rights to different companies to make a Halo MMO, as well as a handheld Halo game. Both of these were never finished.

There are Japanese or Chinese characters on certain weapons throughout the Halo series.