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Assignment of each graph edge of a graph to one of two color classes (commonly designation "red" and "green").

A formula satisfied by all Hamiltonian cycles with n nodes. Let f_j be the number of regions inside the circuit with j sides, and let g_j be the number of regions outside the ...

The problem of deciding if four colors are sufficient to color any map on a plane or sphere.

A symmetric block design (4n+3, 2n+1, n) which is equivalent to a Hadamard matrix of order 4n+4. It is conjectured that Hadamard designs exist for all integers n>0, but this ...

Every graph with n vertices and maximum vertex degree Delta(G)<=k is (k+1)-colorable with all color classes of size |_n/(k+1)_| or [n/(k+1)], where |_x_| is the floor ...

The Hajós number h(G) of a graph G is the maximum k such that G contains a subdivision of the complete graph K_k.

A binary Hamming code H_r of length n=2^r-1 (with r>=2) is a linear code with parity-check matrix H whose columns consist of all nonzero binary vectors of length r, each used ...

The Hamming distance between two vertices of a hypercube is the number of coordinates at which the two vertices differ.

One of the 24 7-polyiamonds.

A heptomino is a 7-polyomino. There are 108 free (illustrated above), 196 one-sided, and 760 fixed heptominoes. There is a single heptomino containing a hole (illustrated ...