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PROJECT EULER · #0812

Dynamical Polynomials

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A dynamical polynomial is a monicleading coefficient is 1 polynomial f(x) with integer coefficients such that f(x) divides f(x22).

For example, f(x)=x2x2 is a dynamical polynomial because f(x22)=x45x2+4=(x2+x2)f(x).

Let S(n) be the number of dynamical polynomials of degree n.
For example, S(2)=6, as there are six dynamical polynomials of degree 2:

x24x+4,x2x2,x24,x21,x2+x1,x2+2x+1

Also, S(5)=58 and S(20)=122087.

Find S(10000). Give your answer modulo 998244353.

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