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A055684
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Number of different n-pointed stars.
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7
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0, 0, 1, 0, 2, 1, 2, 1, 4, 1, 5, 2, 3, 3, 7, 2, 8, 3, 5, 4, 10, 3, 9, 5, 8, 5, 13, 3, 14, 7, 9, 7, 11, 5, 17, 8, 11, 7, 19, 5, 20, 9, 11, 10, 22, 7, 20, 9, 15, 11, 25, 8, 19, 11, 17, 13, 28, 7, 29, 14, 17, 15, 23, 9, 32, 15, 21, 11, 34, 11, 35, 17, 19, 17, 29, 11
(list; graph; refs; listen; history; internal format)
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OFFSET
| 3,5
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COMMENTS
| Does not count rotations or reflections.
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REFERENCES
| Mark A. Herkommer, "Number Theory, A Programmer's Guide," McGraw-Hill, New York, 1999, page 58.
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LINKS
| Alexander Bogomolny, Polygons: formality and intuition.. Includes applet to draw star polygons.
Hugo Pfoertner, Star-shaped regular polygons up to n=25.
Eric Weisstein's World of Mathematics, Star Polygon.
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FORMULA
| ( phi(n) -2 )/2 = A023022 -1.
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EXAMPLE
| The first star has five points and is unique. The next is the seven pointed star and it comes in two varieties.
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MAPLE
| with(numtheory): A055684 := n->(phi(n)-2)/2;
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MATHEMATICA
| Table[(EulerPhi[n]-2)/2, {n, 3, 50}]
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CROSSREFS
| Cf. A023022.
Cf. A053669 smallest skip increment, A102302 skip increment of densest star polygon.
Sequence in context: A193787 A072614 A067044 * A024559 A061797 A068341
Adjacent sequences: A055681 A055682 A055683 * A055685 A055686 A055687
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KEYWORD
| nonn,easy
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 09 2000
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