The spanning-tree factorization conjecture for Sierpinski gaskets

Let SGd(n)SG_d(n) be the dd-dimensional Sierpinski gasket at stage nn, and let fd(n)=NST(SGd(n))f_d(n)=N_{ST}(SG_d(n)) denote its number of spanning trees. Define exponents αd(n)\alpha_d(n), βd(n)\beta_d(n), and γd(n)\gamma_d(n) by

αd(n)=d12[(d+1)n1],\alpha_d(n)=\frac{d-1}{2}\bigl[(d+1)^n-1\bigr], βd(n)=d12d[(d+1)n+1+dn+d1],\beta_d(n)=\frac{d-1}{2d}\bigl[(d+1)^{n+1}+dn+d-1\bigr], γd(n)=d12d[(d+1)ndn1].\gamma_d(n)=\frac{d-1}{2d}\bigl[(d+1)^n-dn-1\bigr].

Spanning-tree factorization conjecture. The number of spanning trees is

fd(n)=2αd(n)(d+1)βd(n)(d+3)γd(n).f_d(n)=2^{\alpha_d(n)}(d+1)^{\beta_d(n)}(d+3)^{\gamma_d(n)}.

This conjecture extends the simple prime-factor formulas established for the two-, three-, and four-dimensional Sierpinski gaskets. The stated exponents are positive integers for positive integer dd and non-negative integer nn, and the formula agrees at n=0n=0 with the spanning-tree count (d+1)d1(d+1)^{d-1} for the complete graph SGd(0)SG_d(0). A general proof or explanatory method for the unexpectedly simple solution is not supplied.

Sources & referencesView supporting material

Primary source

Shu-Chiuan Chang and Lung-Chi Chen, “Spanning trees on the Sierpinski gasket”, arXiv:cond-mat/0609453 (2006).

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