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Monday, October 1, 2012

Next Up, Dyson Numbers


From Dunbar to Dyson...

In an old "TierneyLab" (NY Times) post an anecdote is re-told of genius Freeman Dyson sitting around a table with a bunch of scientists where the question arises, is there an integer such that by moving the last digit to the front (say 1234 to 4123) you can arrive at a result such that the new integer is exactly double the value of the original integer? In a matter of seconds, Dyson essentially responds (to a stunned group), “Oh, that’s not difficult, but of course the smallest such number is 18 digits long.” AND, he was right!

Numbers that can be similarly manipulated in such a manner (employing different multiples) are often called "Dyson Numbers" (also known as "parasitic numbers"), and you can read the original TierneyLab post here:

http://tierneylab.blogs.nytimes.com/2009/04/06/freeman-dysons-4th-grade-math-puzzle/

and a follow-up post to it here:

http://tierneylab.blogs.nytimes.com/2009/04/13/prize-for-dyson-puzzle/


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