olymmath

Putnam 2025 B5

  • Session B

Let pp be a prime number greater than 33. For each k∈{1,…,p−1}k \in \{1,\dots,p-1\}, let I(k)∈{1,2,…,p−1}I(k) \in \{1,2,\dots,p-1\} be such that k⋅I(k)≡1(modp)k \cdot I(k) \equiv 1 \pmod{p}. Prove that the number of integers k∈{1,…,p−2}k \in \{1,\dots,p-2\} such that I(k+1)<I(k)I(k+1) < I(k) is greater than p/4−1p/4-1.

Curated text Kedlaya Putnam archive. Quoted with source.

Solutions

Human solution Solution 1 by Manjul Bhargava, 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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