The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #17 Feb 10 2026 10:09:16
%S 1,4,4,7,10,11,15
%N Covering numbers C(n,6,3).
%C a(13) <= 21.
%D CRC Handbook of Combinatorial Designs, 1996, p. 262.
%H D. Gordon, <a href="http://www.dmgordon.org/cover">La Jolla Repository of Coverings</a>.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Covering_design">Covering design</a>.
%H <a href="/index/Cor#covnum">Index entries for covering numbers</a>.
%K nonn,hard,more
%O 6,2
%A _N. J. A. Sloane_