Is it true that the Boeing 707 got its name because the quantity sqrt(2)/2 was used so much in the plane's design calculations? To four places sqrt(2) is 3.1414.

One of the most frequently asked questions posed to Boeing company historians is, "How did Boeing come up with the 7-7 name for its commercial jets?" There are many myths about the Boeing 7-7 name, one of the most famous brands in history.

People who lean toward math and engineering are certain that 707 was chosen because it is the sine of the angle of wing sweep on a 707. It's not, since the wing sweep is 35 degrees and not 45. However, more people lean toward superstition and feel that the positive connotation of the number seven was the reason it was selected.

The truth is a bit more mundane. Boeing has assigned sequential model numbers to its designs for decades, as have most aircraft manufacturers.

The marketing department decided that "Model 700" did not have a good ring to it for the company's first commercial jet. So they decided to skip ahead to Model 707 because that reiteration seemed a bit catchier.

http://www.boeing.com/news/frontiers/archive/2004/february/i_history.html