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Old 2005-08-31, 22:41   #1
akruppa's Avatar
Aug 2002

2,467 Posts
Default ECM puzzle (hard)

Note: do not attempt to solve this if you are unfamiliar with the internal workings of ECM and its implementations.

This is an oddity I stumbled upon while making a few more test cases for 2^n+-1 numbers for GMP-ECM with the GWNUM stage 1. It caused a bit of puzzlement between Dave and me on the developers mailing list, until Paul Zimmermann completely solved the mystery.

echo 33554520197234177 | ./ecm -sigma 2046841451 372 1

does not find the prime, but

echo 33554520197234177 | ./ecm -sigma 2046841451 373 1

does. However,

echo 33554520197234177 | ./ecm -sigma 2046841451 -go 373 372 1

does not. Why?

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