We classify connected spanning convex subgraphs of the square cycles. We then show that every spanning tree of C 2 n is contained in a unique nontrivial connected spanning convex subgraph of C 2 n . As a result, we obtain a purely combinatorial derivation of the formula for the number of spanning trees of the square cycles.
The exact formula for the average hitting time (HT, as an abbreviation) of simple random walks from one vertex to any other vertex on the square C 2 N of an N -vertex cycle graph CN was given by N. Chair [Journal of Statistical Physics, 154 (2014) 1177-1190. In that paper, the author gives the expression for the even N case and the expression for the odd N case separately. In this paper, by using an elementary method different from Chair (2014), we give a much simpler single formula for the HT's of simple random walks on C 2 N . Our proof is considerably short and fully combinatorial, in particular, has no-need of any spectral graph theoretical arguments. Not only the formula itself but also intermediate results through the process of our proof describe clear relations between the HT's of simple random walks on C 2 N and the Fibonacci numbers.
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