MathDB
2018-2019 Fall OMO Problem 24

Source:

November 7, 2018
Online Math Open

Problem Statement

Let p=101p = 101 and let SS be the set of pp-tuples (a1,a2,,ap)Zp(a_1, a_2, \dots, a_p) \in \mathbb{Z}^p of integers. Let NN denote the number of functions f:S{0,1,,p1}f: S \to \{0, 1, \dots, p-1\} such that
[*] f(a+b)+f(ab)2(f(a)+f(b))(modp)f(a + b) + f(a - b) \equiv 2\big(f(a) + f(b)\big) \pmod{p} for all a,bSa, b \in S, and [*] f(a)=f(b)f(a) = f(b) whenever all components of aba-b are divisible by pp.
Compute the number of positive integer divisors of NN. (Here addition and subtraction in Zp\mathbb{Z}^p are done component-wise.)
Proposed by Ankan Bhattacharya