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Problem #68

A Mixture of Ryski's Problems

Ryski was asked compute the sum of the series

\sum\limits_{k=0}^{∞}(1/((4k + 1)(4k + 2)(4k + 3)(4k + 4))).

Let this summation be p.

Ryski also has 2*n different pens (nN, n ≥ 2). Each day, he takes n pens with him to school. After some days the following condition was fulfilled: every two pens were together on at least one day. Let the minimum number of days needed for this to happen be q.

Give the answer as [p * q * {10^{20}}], where [x] denotes the greatest integer less than or equal to x.

Contributed by Priyanshu Sheth

Solved by 78 users

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