This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A095029 #26 Aug 18 2021 09:36:24
%S A095029 3,6,7,12,14
%N A095029 An example of a (v,k,lambda)=(21,5,1) cyclic difference set.
%C A095029 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. Difference sets with lambda=1 (planar difference sets) have order n=k-1. The Prime Power Conjecture states that all Abelian planar difference sets have order n a prime power. It is known that no cyclic planar difference sets of nonprime power order n exist with n < 2*10^9 (see Baumert, Gordon link)
%H A095029 Leonard D. Baumert and Daniel M. Gordon, <a href="https://arxiv.org/abs/math/0304502">On the existence of cyclic difference sets with small parameters</a>, arXiv:math/0304502 [math.CO], 30 Apr 2003.
%H A095029 Dan Gordon, <a href="http://web.archive.org/web/20101226230341/http://www.ccrwest.org/diffsets/ds_list.pdf">List of Cyclic Difference Sets</a>, (2003).
%H A095029 Dan Gordon, <a href="https://dmgordon.org/diffset">Difference Sets</a>, searchable database.
%e A095029 Representation of {1,...,20}: 1=7-6, 2=14-12, 3=6-3, 4=7-3, 5=12-7, 6=12-6, 7=14-7, 8=14-6, 9=12-3, 10=21+3-14, 11=14-3, 12=21+3-12, 13=21+6-14, 14=21+7-14, 15=21+6-12, 16=21+7-12, 17=21+3-7, 18=21+3-6, 19=21+12-14, 20=21+6-7. - _Hugo Pfoertner_, Aug 13 2011
%Y A095029 Cf. A095025 (number of cyclic difference sets with n elements), A095029-A095047 (more examples of cyclic difference set with k=5..20), A000961 (prime powers).
%K A095029 fini,full,nonn
%O A095029 1,1
%A A095029 _Hugo Pfoertner_, May 27 2004