$$x^{12}-x^7-x^6-x^5+1 = 0\tag1$$

This has Lehmer’s decic polynomial as a factor,

$$x^{10} + x^9 - x^7 - x^6 - x^5 - x^4 - x^3 + x + 1=0\tag2$$

hence one of its roots is the smallest known Salem number. All ten roots obey the beautiful cyclotomic relation,

$$x^{630}-1=\frac{(x^{315}-1)(x^{210}-1)(x^{126}-1)^2(x^{90}-1)(x^{3}-1)^3(x^{2}-1)^5(x-1)^3} {(x^{35}-1)(x^{15}-1)^2(x^{14}-1)^2(x^{5}-1)^6\, x^{68}}$$

found by D. Broadhurst. But this was back in 1999 (paper here). Has anything similar for other Salem numbers been found since then?

  • $\begingroup$ I don't know. Such cyclotomic relations come up in Cremona, J. E., Unimodular integer circulants, Math. Comp. 77 (2008), no. 263, 1639–1652, MR2398785 (2009c:11042), which might be worth a look. $\endgroup$ – Gerry Myerson Mar 1 '12 at 3:15
  • $\begingroup$ @GerryMyerson: I found some relations. $\endgroup$ – Tito Piezas III Jul 30 '15 at 7:15

Revisiting this old question, now armed with Mathematica's "Integer Relations", I find that it is quite easy to look for similar polynomial relations. For example, let $x$ be a root of Lehmer's decic, then it is also the case that,

$$x^{630}-1 = \frac{(x^{315}-1)(x^{210}-1)(x^{126}-1)^2(x^{90}-1)(x^{10}-1)(x^{9}-1)}{(x^{70}-1)(x^{63}-1)(x^{45}-1)(x^{42}-1)(x^{30}-1)(x^{6}-1)}$$

Given the fifth smallest known Salem number $y$ and a root of the decic,



$$y^{210}-1 =\frac{(y^{105}-1)(y^{70}-1)(y^{42}-1)(y^{30}-1)(y^{14}-1)(y^{6}-1)(y^{3}-1)^2}{ (y^{35}-1)(y^{10}-1)(y^{7}-1)^2(y^{2}-1)\,y}$$


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