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Search: id:A141213
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| A141213 |
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Defining A to be the interior angle of a regular polygon, the number of constructible regular polygons such that A is in a field extension = degree 2^n, starting with n=0. This is also the number of values of x such that phi(x)/2 = 2^n (where phi is Euler's phi function), also starting with n=0. |
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1
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| 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 34, 34
(list; graph; listen)
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OFFSET
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0,1
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FORMULA
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For n<=31, f(n)=n+3; for n>=31, f(n)=34.
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EXAMPLE
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For degree 2^0, there are 3 polygons with 3, 4 & 6 sides.
For degree 2^1, there are 4 polygons with 5, 8, 10 & 12 sides.
For degree 2^2 there are 5 polygons with 15, 16, 20, 24 & 30 sides.
For n<=31, for degree 2^n, there are n+3 polygons.
For n>= 31 there are 34 polygons.
Assuming there are only five Fermat primes, the sequence will continue repeating 34 for ever.
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CROSSREFS
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Cf. A141214.
Sequence in context: A004721 A030544 A058321 this_sequence A114637 A009056 A065475
Adjacent sequences: A141210 A141211 A141212 this_sequence A141214 A141215 A141216
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KEYWORD
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nonn
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AUTHOR
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Matthew Lehman (matt.comicopia(AT)gmail.com), Jun 14 2008
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