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1.
Palindromic, sequenced, or repeating numbers on odometers/trip meters.

Doug Grosjean, of IBMWR Presidential fame, has always been fascinated by palindromic or repeating number sequences as they rolled up on the odometer, frequently posting pictures of his speedometer as the odometer and trip meter lined up to make memorable numbers. Who doesn't remember cracking that first 100,000 miles on their vehicle?

While some number combinations are naturally occurring, the chances of other combinations self-occurring are remarkably slim and require preplanning by the watcher. This helps provide some level of interaction with the process, further improving the enjoyment achieved by people wanting to create their own Grosjean Numbers. Having multiple odometers helps improve the difficulty of creating multiple number combinations further decreasing boredom while on those long trips!

A friend's son attending Penn State explained the phenomenon to his math teachers, who quickly adopted Grosjean Numbers within examples of their class work.
Grosjean Number examples can be found on your speedometer

Odometer-/--Trip meter
0123456--/--789.0 => 01234567890
1234565--/--432.1
1111111--/--111.1
1000000--/--000.0
by edeslaur October 06, 2009