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Blanuša Snarks


BlanusaSnarks

The original two Blanuša snarks were the second and third snarks discovered, found by Blanuša (1946). Orbanić et al. (2004) call the first the "Blanuša double" and the second the "Blanuša snark." Tutte wrote of the result, "I saw Blanuša's paper soon after it appeared. Alas, I did not understand the language, but the diagram made all clear!" The original two Blanuša snarks each have 18 vertices and edge chromatic number 4.

BlanusaSnarks3D

The original two Blanuša snarks are illustrated above in three-dimensional graph drawings due to Orbanić et al. (2004). Orbanić et al. (2004) also showed that the first Blanuša snark is of graph genus 2 (i.e., is double-toroidal), while the second has graph genus 1 (i.e., is toroidal).

The Blanuša snarks are used as the logo for the Croatian Mathematical Society (Ivanšić).

The Blanuša snarks are implemented in the Wolfram Language as GraphData[{"BlanusaSnark", {n, k}}] for n=1 to 4 and k=1, 2, with the original two Blanuša snarks corresponding to n=1.

The graph crossing number cr(G), toroidal crossing number cr_1(G), and graph genus gamma(G) of the eight implemented Blanuša snarks are summarized in the following table (E. Weisstein, Sep. 22, 2026). A dash indicates that the value is not available.

(n,k)cr(G)cr_1(G)gamma(G)
(1,1)212
(1,2)201
(2,1)401
(2,2)412
(3,1)401
(3,2)4-2
(4,1)601
(4,2)6-2
BlanusaSnarksTorus

Five of the Blanuša snarks are illustrated above in graph drawings on the torus. The drawings for the (1,2)-, (2,1)-, and (3,1)-Blanuša snarks are torus graph embeddings, while those for the (1,1)- and (2,2)-Blanuša snarks have one crossing and realize toroidal crossing number 1.

BlanusaSnarkMatrices

The plots above show the adjacency, incidence, and distance matrices of the first (top) and second (bottom) Blanuša snarks.

BlanusaSnark1

The first Blanuša snark was found independently in the drawing shown above by Collier and Schmeichel (1978) who erroneously characterized it as a "new cubic hypohamiltonian graph."

BlanusaSnarkSeries

The "first and second Blanuša snarks" are actually the smallest members of two infinite families of snarks of graph order 8n+10, i.e., Blanuša snarks of type 1 and 2 on 18, 26, 34, 42, ... vertices (Read and Wilson 1998, p. 280), illustrated above.

Blanuša snarks are platypus graphs.


See also

Snark, Weak Snark

Portions of this entry contributed by Ed Pegg, Jr. (author's link)

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References

Blanuša, D. "Problem cetiriju boja." Glasnik Mat. Fiz. Astr. Ser. II. 1, 31-42, 1946.Bondy, J. A. and Murty, U. S. R. Graph Theory. Berlin, Germany: Springer-Verlag, p. 462, 2008.Collier, J. B. and Schmeichel, E. F. "Systematic Searches for Hypohamiltonian Graphs." Networks 8, 193-200, 1978.Holton, D. A. and Sheehan, J. The Petersen Graph. Cambridge, England: Cambridge University Press, pp. 82 and 88-89, 1993.House of Graphs. Blanuša Snarks. Blanuša Snark #1, Blanuša Snark #2, Graph 19706, and Graph 19731.Ivanšić, I. "Blanušin Graf." http://www.math.hr/hmd/logo.htm.Orbanić, A.; Pisanski, T.; Randić, M.; and Servatius, B. "Blanuša Double." Math. Commun. 9, 91-103, 2004.Read, R. C. and Wilson, R. J. An Atlas of Graphs. Oxford, England: Oxford University Press, pp. 276 and 280, 1998.West, D. B. Introduction to Graph Theory, 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, p. 305-306, 2000.

Referenced on Wolfram|Alpha

Blanuša Snarks

Cite this as:

Weisstein, Eric W., with contributions by Ed Pegg, Jr.. "Blanuša Snarks." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/BlanusaSnarks.html

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