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An Andreini tessellation is a three-dimensional equivalent of a semiregular tessellation. There are 28 such tessellations.

A term in social choice theory meaning invariance of a result under permutation of voters.

A mathematical statement of the equivalence of two quantities. The equality "A is equal to B" is written A=B.

An operator of period 2, i.e., an operator * which satisfies ((a)^*)^*=a.

A polynomial in which the sum of subscripts is the same in each term.

An obtuse triangle is a triangle in which one of the angles is an obtuse angle. (Obviously, only a single angle in a triangle can be obtuse or it wouldn't be a triangle.) A ...

The alternating group graph AG_n is the undirected Cayley graph of the set of 2(n-2) generators of the alternating group A_n given by g_3^-, g_3^+, g_4^-, g_4^+, ..., g_n^-, ...

The (n,k)-arrangement graph A_(n,k) is defined as the graph on the vertex set consisting of the permutations of {1,2,...,n} containing at most k elements where vertices are ...

Consider an infinite repository containing balls of n different types. Then the following table summarizes the number of distinct ways in which k balls can be picked for four ...

1 0 1 0 1 1 0 1 2 2 0 2 4 5 5 (1) The Entringer numbers E(n,k) (OEIS A008281) are the number of permutations of {1,2,...,n+1}, starting with k+1, which, after initially ...