This number is a composite.
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235235*2^70000-1, a 21078-digit prime number was, for a brief two-week period in late July and early August of 1989, the world's largest-known non-Mersenne prime. It was discovered by the "Amdahl Six" group of John Brown, Landon Curt Noll, Bodo K. Parady, Gene Ward Smith, Joel F. Smith, and Sergio E Zarantonello. [Dobb]