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1/pi =((2*sqrt(2))/9801) sum_(k=0)% 5Einfinity %28%28%284k%29%21%2a%281103%2B%2826390%2ak%29%29%29%2F%28%28%28k28%21%29%5E4%29%2a%28396%29% 5E%284%2ak%29%29%29
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