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A293492
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a(n) is the number of sequences (s_1, ..., s_n) of positive integers such that (Product_{k=1..n} [s_k, -1; 1, 0])^2 = [-1, 0; 0, -1].
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0
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OFFSET
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0,3
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COMMENTS
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Let M(s) denote the matrix
[s, -1]
[+1, 0]
in SL(2,Z). Then we count sequences of positive integers [s_1, ..., s_n] such that (Product_{k=1..n} M(s_k))^2 = -Identity.
This is Problem III in the Ovsienko article.
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LINKS
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CROSSREFS
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Cf. A000984 (counts "totally positive" solutions: Sum_k s_k = 3n-3).
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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