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A number which is simultaneously square and triangular. Let T_n denote the nth triangular number and S_m the mth square number, then a number which is both triangular and ...

Let f be a fractional coloring of a graph G. Then the sum of values of f is called its weight, and the minimum possible weight of a fractional coloring is called the ...

There are a number of attractive compounds of two regular tetrahedra. The most symmetrical is the arrangement whose outer hull is the stella octangula (left figure), while ...

There are a number of attractive polyhedron compounds consisting of 12 octahedra. This compound will be implemented in a future version of the Wolfram Language as ...

There are a number of attractive polyhedron compounds consisting of 13 octahedra. This compound will be implemented in a future version of the Wolfram Language as ...

There are a number of attractive polyhedron compounds consisting of 25 octahedra. These compounds will be implemented in a future version of the Wolfram Language as ...

There are a number of attractive polyhedron compounds consisting of 30 octahedra. This compound will be implemented in a future version of the Wolfram Language as ...

There are a number of attractive polyhedron compounds consisting of 35 octahedra. This compound will be implemented in a future version of the Wolfram Language as ...

The nth Smarandache-Wellin number is formed from the consecutive number sequence obtained by concatenating of the digits of the first n primes. The first few are 2, 23, 235, ...

A Poulet number whose divisors d all satisfy d|2^d-2. The first few are 341, 1387, 2047, 2701, 3277, 4033, 4369, 4681, 5461, 7957, 8321, ... (OEIS A050217).