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A006961
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Mappings from n points to themselves with in-degree <= 2.
(Formerly M2584)
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4
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1, 1, 3, 6, 15, 31, 75, 164, 388, 887, 2092, 4884, 11599, 27443, 65509, 156427, 375263
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| N. G. de Bruijn and D. A. Klarner, Multisets of aperiodic cycles, SIAM J, Algeb. Discrete Meth., 3 (1982), 359-368.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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CROSSREFS
| Cf. A006961.
Sequence in context: A034739 A097941 A117161 * A034740 A152167 A105476
Adjacent sequences: A006958 A006959 A006960 * A006962 A006963 A006964
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KEYWORD
| nonn,easy,nice
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AUTHOR
| Simon Plouffe (simon.plouffe(AT)gmail.com)
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