MathDB
A nice combinatorics from Iranian TST 2017

Source: Iranian TST 2017, first exam day 2, problem 6

April 6, 2017
combinatoricsIranIranian TSTHamiltonian pathcatalan

Problem Statement

In the unit squares of a transparent 1×1001 \times 100 tape, numbers 1,2,,1001,2,\cdots,100 are written in the ascending order.We fold this tape on it's lines with arbitrary order and arbitrary directions until we reach a 1×11 \times1 tape with 100100 layers.A permutation of the numbers 1,2,,1001,2,\cdots,100 can be seen on the tape, from the top to the bottom. Prove that the number of possible permutations is between 21002^{100} and 41004^{100}. (e.g. We can produce all permutations of numbers 1,2,31,2,3 with a 1×31\times3 tape)
Proposed by Morteza Saghafian