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Search: id:A094925
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| A094925 |
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A hexagonal spiral Fibonacci sequence. |
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+0
2
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| 1, 1, 2, 4, 7, 12, 20, 34, 55, 90, 148, 240, 394, 638
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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Consider the following spiral:
..............a(6)..a(7)..a(8)
...........a(5)..a(1)..a(2)..a(9)
........a(14).a(4)..a(3)..a(10)
...........a(13).a(12).a(11)
Then a(1)=1, a(n)=a(n-1)+Sum{a(i) : a(i) adjacent to a(n-1)} Here 6 terms around a(m) touch a(m).
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LINKS
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N. Fernandez, Spiro-Fibonacci numbers
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EXAMPLE
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a(2) = a(1) = 1
a(3) = a(1)+a(2) = 2
a(4) = a(1)+a(2)+a(3) = 4
a(5) = a(1)+a(3)+a(4) = 7
a(6) = a(1)+a(4)+a(5) = 12
a(7) = a(1)+a(5)+a(6) = 20
thus:
............12....20...34
.........7.....1.....1.....55
......638...4.....2.....90
........394....240..148
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CROSSREFS
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Cf. A094926, A078510, A079421, A079422.
Sequence in context: A000071 A093607 A005182 this_sequence A079970 A079816 A100482
Adjacent sequences: A094922 A094923 A094924 this_sequence A094926 A094927 A094928
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KEYWORD
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nonn,easy,more
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AUTHOR
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Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp)
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