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Old 2007-02-22, 22:53   #1
rogue
 
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I just discovered that 137132*5^25323+1 is composite. I assume that a couple of digits in the exponent were transposed, but haven't retested the k.

BTW, I've verified all other Sierpinki and Riesel base 5 candidates for n > 100 with Phil's phrot program. This one showed up as composite while I was testing. It also shows as composite with PFGW.
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Old 2007-02-23, 00:35   #2
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Quote:
Originally Posted by rogue View Post
I just discovered that 137132*5^25323+1 is composite. I assume that a couple of digits in the exponent were transposed...

You were right. Sieved that k from 20000 to 27000 for 1 minute and looked at close matches:

Primality testing 137132*5^25353+1 [N-1, Brillhart-Lehmer-Selfridge]
Running N-1 test using base 2
Calling Brillhart-Lehmer-Selfridge with factored part 99.97%
137132*5^25353+1 is prime! (98.3633s+0.0211s)
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