%I
%S 1,3,5,9,27
%N Size of minimal covering code in {Z_3}^n with covering radius 1 (the next 3 terms are in the ranges 7173, 156186, 402486).
%C Because each codeword covers 2n+1 of the 3^n words, ceil(3^n/(2n+1)) is a lower bound.  _Rob Pratt_, Jan 06 2015
%D G. D. Cohen et al., Covering Codes, NorthHolland, 1997, p. 174.
%H D. Brink, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Brink/brink3.html">The Inverse Football Pool Problem</a>, J. Int. Seq. 14 (2011) # 11.8.8.
%H H. Hamalainen et al., <a href="http://www.jstor.org/stable/2974552">Football pools  a game for mathematicians</a>, Amer. Math. Monthly, 102 (1995), 579588.
%H G. Keri, <a href="http://www.sztaki.hu/~keri/codes">Tables for Bounds on Covering Codes</a>
%H <a href="/index/Coa#covcod">Index entries for sequences related to covering codes</a>
%Y A column of A060439.
%K nonn,hard
%O 1,2
%A _N. J. A. Sloane_.
%E Bounds corrected and corresponding reference added by _Jan Kristian Haugland_, Mar 10 2010
