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A095025
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Number of cyclic difference sets with n elements.
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20
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1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 2, 0, 2, 1, 0, 1, 2, 0, 1, 1, 1, 1, 0, 2, 1, 1, 3, 1, 3, 0, 1, 0, 0, 1, 1, 4, 1, 1, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 1, 6, 0, 2, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0
(list; graph; refs; listen; history; internal format)
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OFFSET
| 3,3
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COMMENTS
| A (v,k,lambda) cyclic difference set is a subset D={d_1,d_2,...,d_k} of the integers modulo v such that {1,2,...,v-1} can each be represented as a difference (d_i-d_j) modulo v in exactly lambda different ways.
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LINKS
| Dan Gordon, La Jolla Difference Set Repository
Len Baumert and Dan Gordon, Papers on Difference Sets
Dan Gordon, List of Cyclic Difference Sets
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EXAMPLE
| a(3)=1 corresponds to the (7,3,1) set {1,2,4}, a(4)=1 corresponds to the (14,4,1) set {0,1,3,9}.
a(5)=2 because there are two cyclic difference sets of length 5: The (v,k,lambda)=(11,5,2) set A095028={1,3,4,5,9} and the (21,5,1) set A095029= {3,6,7,12,14}
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CROSSREFS
| Cf. A095029-A095047 examples of cyclic difference set with k=5..20.
Sequence in context: A098495 A175432 A204118 * A069897 A175597 A181348
Adjacent sequences: A095022 A095023 A095024 * A095026 A095027 A095028
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KEYWORD
| nonn
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AUTHOR
| Hugo Pfoertner (hugo(AT)pfoertner.org), May 27 2004
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