olymmath

Putnam 2017 B4

  • Session B

Evaluate the sum

∑k=0∞(3⋅ln⁡(4k+2)4k+2−ln⁡(4k+3)4k+3−ln⁡(4k+4)4k+4−ln⁡(4k+5)4k+5)=3⋅ln⁡22−ln⁡33−ln⁡44−ln⁡55+3⋅ln⁡66−ln⁡77−ln⁡88−ln⁡99+3⋅ln⁡1010−⋯ .\begin{gathered}\sum_{k=0}^\infty \left( 3 \cdot \frac{\ln(4k+2)}{4k+2} - \frac{\ln(4k+3)}{4k+3} - \frac{\ln(4k+4)}{4k+4} - \frac{\ln(4k+5)}{4k+5} \right) \\ = 3 \cdot \frac{\ln 2}{2} - \frac{\ln 3}{3} - \frac{\ln 4}{4} - \frac{\ln 5}{5} + 3 \cdot \frac{\ln 6}{6} - \frac{\ln 7}{7} \\ - \frac{\ln 8}{8} - \frac{\ln 9}{9} + 3 \cdot \frac{\ln 10}{10} - \cdots .\end{gathered}

(As usual, ln⁡x\ln x denotes the natural logarithm of xx.)

Curated text Kedlaya Putnam archive. Quoted with source.

Solutions

Human solution Solution 1 by Kiran Kedlaya and Lenny Ng

The terms of the source let olymmath link to this solution but not copy it. Read the solution (Kedlaya Putnam archive).

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