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A095025 Number of cyclic difference sets with n elements. 20
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; text; internal format)
OFFSET

3,3

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.

LINKS

Table of n, a(n) for n=3..100.

Dan Gordon, La Jolla Difference Set Repository

Len Baumert and Dan Gordon, Papers on Difference Sets

Dan Gordon, List of Cyclic Difference Sets

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}

CROSSREFS

Cf. A095029-A095047 examples of cyclic difference set with k=5..20.

Sequence in context: A098495 A175432 A204118 * A274382 A318997 A069897

Adjacent sequences:  A095022 A095023 A095024 * A095026 A095027 A095028

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, May 27 2004

STATUS

approved

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Last modified July 23 19:33 EDT 2019. Contains 325263 sequences. (Running on oeis4.)