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Work began in August 1948 , and the first version was operational by April 1949 ; a program written to search for Mersenne primes ran error-free for nine hours on the night of 16/17 June 1949 .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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