%I #8 Jun 04 2021 14:45:38
%S 1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,6,6,6,6,7,7,7,7,8,8,8,8,9,9,9,
%T 9,10,10,10,10,11,11,11,11,12,12,12,12,13,13,13,13,14,14,14,14,15,15,
%U 15,15,16,16,16,16,17,17,17,17,18,18,18,18,19,19,19,19,20,20,20,20,21,21
%N Duplicate of A008621.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/GraphThickness.html">Graph Thickness</a>
%F G.f.: x(1+x^3-x^4)/((1-x)^2(1+x)(1+x^2)). - _R. J. Mathar_, Sep 12 2008
%t Ceiling[(n+1)/4]
%Y Cf. A002265, A128929.
%K dead
%O 1,4
%A _Eric W. Weisstein_, Sep 09 2008