Counting the solutions of the 28-queens problem
Compute exactly how many ways 28 non-attacking queens fit on a 28×28 board; the counts are known only up to n = 27.
Problems
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Matching problems
Counting Langford pairings for 31 and 32 pairs
Compute the exact number of Langford pairings of order 31 and 32, estimated near 5×10^24 and 9×10^25; counts are known up to order 28.