%I #9 Dec 30 2019 15:03:34
%S 1,4,4,7,10,11,15
%N Covering numbers C(n,6,3) (next term is <= 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 <a href="/index/Cor#covnum">Index entries for covering numbers</a>
%K nonn,hard
%O 6,2
%A _N. J. A. Sloane_.