versions: 2.7.2 and 2.6.2
The isprime() function may return an incorrect result.
436^56-35 is a prime number, but isprime(436^56-35) returns 0.
Here is the transcript:
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> \v
GP/PARI CALCULATOR Version 2.7.2 (released)
i686 running mingw (ix86/GMP-5.1.3 kernel) 32-bit version
compiled: Sep 15 2014, gcc version 4.6.3 (GCC)
threading engine: single
(readline v6.2 enabled, extended help enabled)
> isprime(436^56-35)
%14 = 0
> isprime(436^56-35,1)
%15 =
[ 2 2 1]
[ 5 2 1]
[ 43 2 1]
[ 97 2 1]
[ 239 2 1]
[ 8093 2 1]
[ 33715719073 2 1]
[ 510380473013 2 1]
[ 730919206243 2 1]
[16731483575647 2 1]
> isprime(436^56-35,2)
%16 = 0
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I checked that an older version 2.4.2 returns the correct result.