8 21

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8_20

9_1

Contents

Image:8 21.gif
(KnotPlot image)

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Visit 8_21's page at Knotilus!

Visit 8 21's page at the original Knot Atlas!


[edit] Knot presentations

Planar diagram presentation X1425 X3849 X12,6,13,5 X13,16,14,1 X9,14,10,15 X15,10,16,11 X6,12,7,11 X7283
Gauss code -1, 8, -2, 1, 3, -7, -8, 2, -5, 6, 7, -3, -4, 5, -6, 4
Dowker-Thistlethwaite code 4 8 -12 2 14 -6 16 10
Conway Notation [21,21,2-]


Minimum Braid Representative A Morse Link Presentation An Arc Presentation
Image:BraidPart3.gifImage:BraidPart3.gifImage:BraidPart3.gifImage:BraidPart0.gifImage:BraidPart1.gifImage:BraidPart1.gifImage:BraidPart0.gifImage:BraidPart0.gif
Image:BraidPart4.gifImage:BraidPart4.gifImage:BraidPart4.gifImage:BraidPart3.gifImage:BraidPart2.gifImage:BraidPart2.gifImage:BraidPart3.gifImage:BraidPart3.gif
Image:BraidPart0.gifImage:BraidPart0.gifImage:BraidPart0.gifImage:BraidPart4.gifImage:BraidPart0.gifImage:BraidPart0.gifImage:BraidPart4.gifImage:BraidPart4.gif

Length is 8, width is 3,

Braid index is 3

Image:8 21_ML.gif Image:8 21_AP.gif
[{9, 3}, {2, 7}, {6, 8}, {7, 9}, {4, 1}, {3, 6}, {5, 2}, {8, 4}, {1, 5}]

[edit Notes on presentations of 8 21]

Knot 8_21.
Knot 8_21.
A graph: knot 8_21.
A graph: knot 8_21.
A part of a knot and a part of a graph.
A part of a knot and a part of a graph.

[edit] Three dimensional invariants

Symmetry type Reversible
Unknotting number 1
3-genus 2
Bridge index 3
Super bridge index 4
Nakanishi index 1
Maximal Thurston-Bennequin number [-9][1]
Hyperbolic Volume 6.78371
A-Polynomial See Data:8 21/A-polynomial

[edit Notes for 8 21's three dimensional invariants]

[edit] Four dimensional invariants

Smooth 4 genus 1
Topological 4 genus 1
Concordance genus 2
Rasmussen s-Invariant -2

[edit Notes for 8 21's four dimensional invariants]

[edit] Polynomial invariants

Alexander polynomial t2 + 4t−5 + 4t−1t−2
Conway polynomial 1−z4
2nd Alexander ideal (db, data sources) {1}
Determinant and Signature { 15, -2 }
Jones polynomial 2q−1−2q−2 + 3q−3−3q−4 + 2q−5−2q−6 + q−7
HOMFLY-PT polynomial (db, data sources) z2a6 + a6z4a4−3z2a4−3a4 + 2z2a2 + 3a2
Kauffman polynomial (db, data sources) z4a8−2z2a8 + 2z5a7−5z3a7 + 2za7 + z6a6z4a6a6 + 3z5a5−6z3a5 + 4za5 + z6a4−2z4a4 + 5z2a4−3a4 + z5a3z3a3 + 2za3 + 3z2a2−3a2
The A2 invariant q22−2q14q12q10 + q8 + 2q6 + q4 + 2q2
The G2 invariant q114q112 + 2q110−3q108 + q104−4q102 + 5q100−4q98 + 3q96 + q94−4q92 + 5q90−2q88 + 2q86 + 2q84−4q82 + 4q80 + 2q78−2q76 + 4q74−4q72 + 3q70−4q66 + 3q64−7q62 + 5q60−4q58−3q56 + 2q54−6q52 + 4q50−5q48q46 + 2q44−3q42 + 2q40−3q36 + 7q34−2q32 + 3q28−3q26 + 7q24−2q22 + 2q20 + q18q16 + 4q14q12 + 2q10 + q8

[edit] "Similar" Knots (within the Atlas)

Same Alexander/Conway Polynomial: {10_136,}

Same Jones Polynomial (up to mirroring, q\leftrightarrow q^{-1}): {}

[edit] Vassiliev invariants

V2 and V3: (0, 1)

[edit] Khovanov Homology

The coefficients of the monomials trqj are shown, along with their alternating sums χ (fixed j, alternation over r). The squares with yellow highlighting are those on the "critical diagonals", where j−2r = s + 1 or j−2r = s−1, where s = -2 is the signature of 8 21. Nonzero entries off the critical diagonals (if any exist) are highlighted in red.   
\ r
  \  
j \
-6-5-4-3-2-10χ
-1      22
-3     110
-5    21 1
-7   11  0
-9  12   -1
-11 11    0
-13 1     -1
-151      1
Integral Khovanov Homology

(db, data source)

  
\dim{\mathcal G}_{2r+i}\operatorname{KH}^r_{\mathbb Z} i = −3 i = −1
r = −6 {\mathbb Z}
r = −5 {\mathbb Z}\oplus{\mathbb Z}_2 {\mathbb Z}
r = −4 {\mathbb Z}\oplus{\mathbb Z}_2 {\mathbb Z}
r = −3 {\mathbb Z}^{2}\oplus{\mathbb Z}_2 {\mathbb Z}
r = −2 {\mathbb Z}\oplus{\mathbb Z}_2^{2} {\mathbb Z}^{2}
r = −1 {\mathbb Z}\oplus{\mathbb Z}_2 {\mathbb Z}
r = 0 {\mathbb Z}\oplus{\mathbb Z}_2 {\mathbb Z}^{2}

[edit] The Coloured Jones Polynomials

[edit] Computer Talk

Much of the above data can be recomputed by Mathematica using the package KnotTheory`. See A Sample KnotTheory` Session, or any of the Computer Talk sections above.

[edit] Modifying This Page

Read me first: Modifying Knot Pages

See/edit the Rolfsen Knot Page master template (intermediate).

See/edit the Rolfsen_Splice_Base (expert).

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