olymmath

HMMT November 2011 H5

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For any finite sequence of positive integers π\pi, let S(π)S(\pi) be the number of strictly increasing subsequences in π\pi with length 2 or more. For example, in the sequence π={3,1,2,4}\pi=\{3,1,2,4\}, there are five increasing sub-sequences: {3,4},{1,2},{1,4},{2,4}\{3,4\},\{1,2\},\{1,4\},\{2,4\}, and {1,2,4}\{1,2,4\}, so S(π)=5S(\pi)=5. In an eight-player game of Fish, Joy is dealt six cards of distinct values, which she puts in a random order π\pi from left to right in her hand. Determine

∑πS(π)\sum_{\pi} S(\pi)

where the sum is taken over all possible orders π\pi of the card values.

Dataset text NuminaMath olympiads. Quoted with source.

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