I have been working for quite a while on finding closed, simple expressions for primitive roots of unity, that is finding solutions of cyclotomic polynomials by radical expressions in the case of constructible regular polygons.
The long-term goal is to find solutions for the 5th, 17th, 257th, and 65537th root of unity, and to better understand relationship between coefficients.
Below some roots already computed, expressed as minimal, regular nested expressions.
This is an onging project.
Primitive 5th Root of Unity \(\sqrt[5]{1}\)
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-\frac{1}{4}& \ \\[10pt]+\frac{1}{4}& \ \sqrt{5\,}\\[10pt]+\frac{1}{4}& \ \sqrt{\!-\!10\!-\!2\sqrt{5\,}\,}\\
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Primitive 17th Root of Unity \(\sqrt[17]{1}\)
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-\frac{1}{16}& \ \\[10pt]+\frac{1}{16}& \ \sqrt{17\,}\\[10pt]+\frac{1}{16}& \ \sqrt{34\!-\!2\sqrt{17\,}\,}\\[10pt]+\frac{1}{8}& \ \sqrt{17\!+\!3\sqrt{17\,}\!-\!\sqrt{170\!+\!38\sqrt{17\,}\,}\,}\\[10pt]+\frac{1}{8}& \ \sqrt{\!-\!34\!+\!2\sqrt{17\,}\!-\!2\sqrt{34\!-\!2\sqrt{17\,}\,}\!+\!4\sqrt{17\!+\!3\sqrt{17\,}\!+\!\sqrt{170\!+\!38\sqrt{17\,}\,}\,}\,}\\
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Primitive 257th Root of Unity \(\sqrt[257]{1}\)
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\begin{split}
-\frac{1}{256}& \ \\[10pt]+\frac{1}{256}& \ \sqrt{257\,}\\[10pt]+\frac{1}{256}& \ \sqrt{514\!-\!2\sqrt{257\,}\,}\\[10pt]+\frac{1}{128}& \ \sqrt{257\!+\!15\sqrt{257\,}\!+\!\sqrt{58082\!+\!3614\sqrt{257\,}\,}\,}\\[10pt]+\frac{1}{128}& \ \sqrt{514\!-\!18\sqrt{257\,}\!+\!6\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{12593\!-\!561\sqrt{257\,}\!+\!\sqrt{21794114\!-\!552002\sqrt{257\,}\,}\,}\,}\\[10pt]+\frac{1}{64}& \ \sqrt{257\!-\!\sqrt{257\,}\!-\!\sqrt{12850\!-\!754\sqrt{257\,}\,}\!+\!2\sqrt{3341\!-\!109\sqrt{257\,}\!-\!\sqrt{6509810\!-\!268274\sqrt{257\,}\,}\,}\!-\!2\sqrt{10794\!+\!70\sqrt{257\,}\!-\!2\sqrt{16703458\!-\!380386\sqrt{257\,}\,}\!-\!4\sqrt{4535793\!+\!253711\sqrt{257\,}\!-\!\sqrt{36803719442626\!+\!2282091196478\sqrt{257\,}\,}\,}\,}\,}\\[10pt]+\frac{1}{64}& \ \sqrt{\begin{aligned}514& \ \!+\!14\sqrt{257\,}\!+\!6\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{4369\!+\!15\sqrt{257\,}\!+\!\sqrt{9112706\!-\!354178\sqrt{257\,}\,}\,}\!-\!4\sqrt{4626\!+\!286\sqrt{257\,}\!+\!10\sqrt{247234\!+\!15422\sqrt{257\,}\,}\!+\!4\sqrt{3314529\!+\!206751\sqrt{257\,}\!+\!\sqrt{20768537086978\!+\!1295505749246\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!-\!8\sqrt{3341\!+\!139\sqrt{257\,}\!+\!35\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!2\sqrt{1306845\!+\!53283\sqrt{257\,}\!-\!\sqrt{257924604274\!+\!4074182542\sqrt{257\,}\,}\,}\!-\!2\sqrt{3682810\!+\!172118\sqrt{257\,}\!+\!10\sqrt{12461428850\!+\!278588558\sqrt{257\,}\,}\!+\!4\sqrt{1185667505937\!+\!67520656239\sqrt{257\,}\!+\!\sqrt{375570632850308163054146\!+\!22763424315321766000318\sqrt{257\,}\,}\,}\,}\,}\end{aligned}\,}\\[10pt]+\frac{1}{32}& \ \sqrt{\begin{aligned}257& \ \!-\!\sqrt{257\,}\!-\!\sqrt{514\!-\!2\sqrt{257\,}\,}\!-\!2\sqrt{257\!+\!15\sqrt{257\,}\!+\!\sqrt{58082\!+\!3614\sqrt{257\,}\,}\,}\!+\!6\sqrt{514\!-\!18\sqrt{257\,}\!+\!6\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{12593\!-\!561\sqrt{257\,}\!+\!\sqrt{21794114\!-\!552002\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!-\!4\sqrt{1285\!-\!5\sqrt{257\,}\!-\!5\sqrt{12850\!-\!754\sqrt{257\,}\,}\!+\!10\sqrt{3341\!-\!109\sqrt{257\,}\!-\!\sqrt{6509810\!-\!268274\sqrt{257\,}\,}\,}\!+\!2\sqrt{442554\!-\!13642\sqrt{257\,}\!+\!6\sqrt{4595699186\!-\!281900018\sqrt{257\,}\,}\!+\!4\sqrt{18581190721\!-\!1150035777\sqrt{257\,}\!+\!\sqrt{668627414781813055490\!-\!41706825763650297602\sqrt{257\,}\,}\,}\,}\,}\\[-10pt]& \ \!-\!4\sqrt{\begin{aligned}2570& \ \!+\!70\sqrt{257\,}\!+\!14\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{57825\!-\!1985\sqrt{257\,}\!-\!\sqrt{2795782210\!-\!132283202\sqrt{257\,}\,}\,}\!+\!4\sqrt{181442\!+\!7022\sqrt{257\,}\!+\!2\sqrt{6216147922\!+\!319198766\sqrt{257\,}\,}\!+\!4\sqrt{4246573681\!+\!229781647\sqrt{257\,}\!+\!\sqrt{30446471517567866434\!+\!1879434198946564798\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!-\!8\sqrt{\begin{aligned}122589& \ \!+\!5467\sqrt{257\,}\!+\!\sqrt{1610477650\!+\!75821486\sqrt{257\,}\,}\!+\!2\sqrt{2191066093\!+\!112238867\sqrt{257\,}\!+\!\sqrt{64430671830932914\!-\!4003622352651442\sqrt{257\,}\,}\,}\\[-10pt]& \ \!+\!2\sqrt{6266752250\!+\!360810454\sqrt{257\,}\!+\!2\sqrt{9280107224736158882\!+\!576107110307438686\sqrt{257\,}\,}\!+\!4\sqrt{4888235774502554705\!+\!303319711244318255\sqrt{257\,}\!+\!\sqrt{41347019429866775450521689114664709954\!+\!2579115892125395493567343388815241662\sqrt{257\,}\,}\,}\,}\end{aligned}\,}\end{aligned}\,}\end{aligned}\,}
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}\)
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\begin{split}
+\frac{1}{32}& \ \sqrt{\begin{aligned}\!-\!514& \ \!+\!2\sqrt{257\,}\!+\!2\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{257\!+\!15\sqrt{257\,}\!+\!\sqrt{58082\!+\!3614\sqrt{257\,}\,}\,}\!+\!4\sqrt{514\!-\!18\sqrt{257\,}\!+\!6\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{12593\!-\!561\sqrt{257\,}\!+\!\sqrt{21794114\!-\!552002\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!-\!8\sqrt{257\!-\!\sqrt{257\,}\!-\!\sqrt{12850\!-\!754\sqrt{257\,}\,}\!+\!2\sqrt{3341\!-\!109\sqrt{257\,}\!-\!\sqrt{6509810\!-\!268274\sqrt{257\,}\,}\,}\!-\!2\sqrt{10794\!+\!70\sqrt{257\,}\!-\!2\sqrt{16703458\!-\!380386\sqrt{257\,}\,}\!-\!4\sqrt{4535793\!+\!253711\sqrt{257\,}\!-\!\sqrt{36803719442626\!+\!2282091196478\sqrt{257\,}\,}\,}\,}\,}\\[-10pt]& \ \!+\!8\sqrt{\begin{aligned}514& \ \!+\!14\sqrt{257\,}\!+\!6\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{4369\!+\!15\sqrt{257\,}\!+\!\sqrt{9112706\!-\!354178\sqrt{257\,}\,}\,}\!-\!4\sqrt{4626\!+\!286\sqrt{257\,}\!+\!10\sqrt{247234\!+\!15422\sqrt{257\,}\,}\!+\!4\sqrt{3314529\!+\!206751\sqrt{257\,}\!+\!\sqrt{20768537086978\!+\!1295505749246\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!+\!8\sqrt{3341\!+\!139\sqrt{257\,}\!+\!35\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!2\sqrt{1306845\!+\!53283\sqrt{257\,}\!-\!\sqrt{257924604274\!+\!4074182542\sqrt{257\,}\,}\,}\!-\!2\sqrt{3682810\!+\!172118\sqrt{257\,}\!+\!10\sqrt{12461428850\!+\!278588558\sqrt{257\,}\,}\!+\!4\sqrt{1185667505937\!+\!67520656239\sqrt{257\,}\!+\!\sqrt{375570632850308163054146\!+\!22763424315321766000318\sqrt{257\,}\,}\,}\,}\,}\end{aligned}\,}\\[-10pt]& \ \!+\!16\sqrt{\begin{aligned}257& \ \!-\!\sqrt{257\,}\!-\!\sqrt{514\!-\!2\sqrt{257\,}\,}\!-\!2\sqrt{257\!+\!15\sqrt{257\,}\!+\!\sqrt{58082\!+\!3614\sqrt{257\,}\,}\,}\!+\!6\sqrt{514\!-\!18\sqrt{257\,}\!+\!6\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{12593\!-\!561\sqrt{257\,}\!+\!\sqrt{21794114\!-\!552002\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!+\!4\sqrt{1285\!-\!5\sqrt{257\,}\!-\!5\sqrt{12850\!-\!754\sqrt{257\,}\,}\!+\!10\sqrt{3341\!-\!109\sqrt{257\,}\!-\!\sqrt{6509810\!-\!268274\sqrt{257\,}\,}\,}\!+\!2\sqrt{442554\!-\!13642\sqrt{257\,}\!+\!6\sqrt{4595699186\!-\!281900018\sqrt{257\,}\,}\!+\!4\sqrt{18581190721\!-\!1150035777\sqrt{257\,}\!+\!\sqrt{668627414781813055490\!-\!41706825763650297602\sqrt{257\,}\,}\,}\,}\,}\\[-10pt]& \ \!-\!4\sqrt{\begin{aligned}2570& \ \!+\!70\sqrt{257\,}\!+\!14\sqrt{514\!-\!2\sqrt{257\,}\,}\!+\!4\sqrt{57825\!-\!1985\sqrt{257\,}\!-\!\sqrt{2795782210\!-\!132283202\sqrt{257\,}\,}\,}\!+\!4\sqrt{181442\!+\!7022\sqrt{257\,}\!+\!2\sqrt{6216147922\!+\!319198766\sqrt{257\,}\,}\!+\!4\sqrt{4246573681\!+\!229781647\sqrt{257\,}\!+\!\sqrt{30446471517567866434\!+\!1879434198946564798\sqrt{257\,}\,}\,}\,}\\[-10pt]& \ \!+\!8\sqrt{\begin{aligned}122589& \ \!+\!5467\sqrt{257\,}\!+\!\sqrt{1610477650\!+\!75821486\sqrt{257\,}\,}\!+\!2\sqrt{2191066093\!+\!112238867\sqrt{257\,}\!+\!\sqrt{64430671830932914\!-\!4003622352651442\sqrt{257\,}\,}\,}\\[-10pt]& \ \!+\!2\sqrt{6266752250\!+\!360810454\sqrt{257\,}\!+\!2\sqrt{9280107224736158882\!+\!576107110307438686\sqrt{257\,}\,}\!+\!4\sqrt{4888235774502554705\!+\!303319711244318255\sqrt{257\,}\!+\!\sqrt{41347019429866775450521689114664709954\!+\!2579115892125395493567343388815241662\sqrt{257\,}\,}\,}\,}\end{aligned}\,}\end{aligned}\,}\end{aligned}\,}\end{aligned}\,}
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Adrian Turtschi, Jan 2008; updated Oct 2020