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SWAC Computes New Mersenne Primes

Five new Mersenne primes

An early electronic computer called the SWAC was used to find the five largest prime numbers known as of 1950.

SWAC Computes New Mersenne Primes

The SWAC (an acronym for Standards Western Automatic Computer) was an early electronic digital computer built in 1950 by the U.S. National Bureau of Standards (the previous name for the present National Institute of Standards and Technology) in Los Angeles. At the time of its completion in August 1950, it was the fastest computer in the world. In January 1952, mathematician Raphael Robinson used the SWAC to discover five new Mersenne primes, i.e. prime numbers of the form 2^n–1, with n = 521, 607, 1279, 2203 and 2281. Upon their discovery, these numbers were the largest known prime numbers, having 157, 183, 386, 664 and 687 digits, respectively. One of the computer's electrostatic memory tubes is preserved and displayed as part of the Computer History Exhibits at the Gates Computer Science building at Stanford University.

Artifact origin

Los Angeles, United States


Primes timeline The Sieve of Eratosthenes Cataldi's Divisor Table Guldin's Factor Table Van Schooten's Prime Table Turing's Zeta Function Machine SWAC Computes New Mersenne Primes

Interactive Content

Computational Explanation

Other Resources

Additional Reading

  • Huskey, H. D. Harry D. Huskey: His Story. BookSurge Publishing, 2004.
  • Office of Naval Research, Arlington Virginia. Digital Computer Newsletter, Vol. 4, No. 2, p. 3, April 1952.
  • Rutland, D. Why Computers are Computers: The SWAC and the PC. Wren Publishers, 1995.
  • Rutland, D. "The SWAC: First Computer on the West Coast." The Analytical Engine, Vol. 4, No. 1, pp. 31–34, 1997.

Image Credits

National Institute of Standards and Technology, Wikimedia