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A058050
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a(n) is the number of different graphs drawn in the following way: you decide for each number k <= n a pair of positive numbers (x(k),y(k)) such that x(k)+y(k)=k; you draw n points numbered 1 to n; draw two arrows from n, one to x(n) and one to y(n); draw two arrows from each k already reached by an arrow, one to x(k) and one to y(k). The process stops when 1 is the only point reached by an arrow without any arrow leaving it; you can also erase the isolated points.
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1, 1, 1, 2, 3, 6, 11, 22, 43, 87, 176, 357, 732, 1497, 3089, 6335, 13099, 26956, 55779, 114904, 237734, 490096, 1013276, 2089105, 4315487, 8894624, 18356468, 37813944, 77958972
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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EXAMPLE
| a(5)=3: there are two possibilities to cut 5, i.e. (1,4) and (2,3); (1,4) gives two possibility to draw such a graph because 4 has also two way of cutting: (2,2) and (1,4); (2,3) gives one possibility; and 2+1=3
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CROSSREFS
| Sequence in context: A124973 A043327 A005578 * A026418 A063895 A027214
Adjacent sequences: A058047 A058048 A058049 * A058051 A058052 A058053
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KEYWORD
| nonn
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AUTHOR
| Mathieu Dupont (mathieudupont(AT)usa.net), Nov 18 2000
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