Circular Logic II (noch nicht übersetzt)

Problem 703

Given an integer n, n3, let B={false,true} and let Bn be the set of sequences of n values from B. The function f from Bn to Bn is defined by f(b1bn)=c1cn where:

  • ci=bi+1 for 1i<n.
  • cn=b1AND(b2XORb3), where AND and XOR are the logical AND and exclusive OR operations.

Let S(n) be the number of functions T from Bn to B such that for all x in Bn, T(x) AND T(f(x))=false. You are given that S(3)=35 and S(4)=2118.

Find S(20). Give your answer modulo 1001001011.