| Blanuša snarks | |
| Vertices: | 18 (both) |
| Edges: | 27 (both) |
| Chromatic Number: | 3 (both) |
| Chromatic Index: | 4 (both) |
| Diameter: | 4 (both) |
| Radius: | 4 (both) |
| Girth: | 5 (both) |
| Automorphisms: | 8, D4 (1st) 4, Klein group (2nd) |
| Properties: | Snark (both) Hypohamiltonian (both) Cubic (both) Toroidal (only one)[1] |
| Book Thickness: | 3 (both) |
| Queue Number: | 2 (both) |
In the mathematical field of graph theory, the Blanuša snarks are two 3-regular graphs with 18 vertices and 27 edges. They were discovered by Yugoslavian mathematician Danilo Blanuša in 1946 and are named after him.[2] When discovered, only one snark was known—the Petersen graph.
As snarks, the Blanuša snarks are connected, bridgeless cubic graphs with chromatic index equal to 4. Both of them have chromatic number 3, diameter 4 and girth 5. They are non-hamiltonian but are hypohamiltonian.[3] Both have book thickness 3 and queue number 2.[4]
The automorphism group of the first Blanuša snark is of order 8 and is isomorphic to the Dihedral group D4, the group of symmetries of a square.
The automorphism group of the second Blanuša snark is an abelian group of order 4 isomorphic to the Klein four-group, the direct product of the Cyclic group Z/2Z with itself.
The characteristic polynomial of the first and the second Blanuša snark are respectively :
(x-3)(x-1)3(x+1)(x+2)(x4+x3-7x2-5x+6)(x4+x3-5x2-3x+4)2
(x-3)(x-1)3(x3+2x2-3x-5)(x3+2x2-x-1)(x4+x3-7x2-6x+7)(x4+x3-5x2-4x+3).
There exists a generalisation of the first and second Blanuša snark in two infinite families of snarks of order 8n+10 denoted
| 1 | |
| B | |
| n |
| 2 | |
| B | |
| n |
In 2007, J. Mazák proved that the circular chromatic index of the type 1 generalized Blanuša snarks
| 1 | |
| B | |
| n |
| 3+{ | 2 |
| n |
In 2008, M. Ghebleh proved that the circular chromatic index of the type 2 generalized Blanuša snarks
| 2 | |
| B | |
| n |
| 3+{ | 1 |
| \lfloor1+3n/2\rfloor |