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A094925
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A hexagonal spiral Fibonacci sequence.
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1
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1, 1, 2, 4, 7, 12, 20, 34, 55, 90, 148, 240, 394, 638, 1043, 1688, 2750, 4450, 7232, 11736, 19002, 30827, 49884, 80856, 130978, 211982, 343348, 555964, 899706, 1456702, 2358089, 3815834, 6176654, 9996926, 16176330, 26180456, 42368468, 68567892
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| 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
| N. Fernandez, Spiro-Fibonacci numbers
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EXAMPLE
| 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
| Cf. A094926, A078510, A079421, A079422.
Sequence in context: A093607 A005182 A172524 * A186537 A079970 A079816
Adjacent sequences: A094922 A094923 A094924 * A094926 A094927 A094928
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KEYWORD
| nonn,easy
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AUTHOR
| Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp)
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EXTENSIONS
| a(15) - a(38) from Nathaniel Johnston (nathaniel(AT)nathanieljohnston.com), Apr 26 2011
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