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Search: id:A140526
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| A140526 |
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Number of derangements of n elements with one pair repeated exactly once (e.g. "ABABCDEF"). |
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+0
1
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| 1, 4, 29, 230, 2033, 19744, 209581, 2418226, 30173825, 405194012, 1535140765, 89520810334
(list; graph; listen)
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OFFSET
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4,2
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LINKS
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Hugo M. Spinelli, Program code related to this sequence
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EXAMPLE
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a(4)=1 because "aabb" has only one derangement: "bbaa";
a(5)=4 because "aabbc" has four derangements: "bbaca", "bbcaa", "bcaab" and "cbaab".
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CROSSREFS
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Cf. A105927 for derangements with an element repeated exactly once and no other repetition (e.g. "AABCDEF"); A105928 for derangements with an element appearing three times and no other repetition (e.g. "AAABCDEF").
Adjacent sequences: A140523 A140524 A140525 this_sequence A140527 A140528 A140529
Sequence in context: A135429 A079756 A087809 this_sequence A125808 A083072 A127770
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KEYWORD
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more,nonn,nice
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AUTHOR
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Hugo M. Spinelli (woodcroft(AT)poli.ufrj.br), Jul 02 2008, Jul 25 2008
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