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PUZZLET 174

A Sequence from Odd, Even & Prime Numbers

Take an integer n of length at least two digits. If n is even, divide by 2; if it's odd, add it to the nearest prime number greater than itself. If the result of either operation is just a single digit integer, the series terminates.   If not, go around again.

Example:  13, 30, 15, 32, 16, 8

What's the longest chain required to complete any sequence starting with a 2-digit integer?  Or to complete a 3- or 4-digit integer sequence?


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Last Updated: January 17th, 2010.