ISL 2010 C3
2500 chess kings have to be placed on a chessboard so that (i) no king can capture any other one (i.e. no two kings are placed in two squares sharing a common vertex); (ii) each row and each column contains exactly 25 kings. Find the number of such arrangements. (Two arrangements differing by rotation or symmetry are supposed to be different.) (Russia)
Official text Transcription from NuminaMath olympiads, checked word for word against the official paper. Quoted with source.
Official text: IMO 2010 Shortlist booklet, page 29.
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Official solution Solution 1 by the IMO Problem Selection Committee
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