239

This number is a prime.

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In 1706, Machin discovered that π/4 = 4 arctan(1/5) - arctan(1/239). Shanks used this to calculate π to 707 places in 1873, but only the first 527 digits were correct.

Submitted: 1999-09-02 23:40:00; Last Modified: 2012-06-15 20:19:57.