%I
%S 1,1,1,2,3,4,2,12,8,4,38,30,14,6,130,80,32,12,500,326,150,66,18,4,944,
%T 460,166,56,12,6,2036,890,304,120,20,10,2,2678,974,362,100,36,4,2,
%U 4892,2114,684,238,68,22,4,16318,6350,2286,836,330,108,24,12,31980,12252
%N Number of perfect rulers with length n (n>=0).
%C For definitions, references and links related to complete rulers see A103294.
%C The values for n=208213 are 22,0,0,0,4,4 according to Arch D. Robison. The values for 199207 are not yet known.  _Peter Luschny_, Feb 20 2014, Jun 28 2019
%C Zero values at 135, 136, 149, 150, 151, 164, 165, 166, 179, 180, 181, 195, 196, 209, 210, 211.  _Ed Pegg Jr_, Jun 23 2019 [These values were found by Arch D. Robison, see links. _Peter Luschny_, Jun 28 2019]
%H Peter Luschny (0..123) and Arch D. Robison (124..198), <a href="/A103300/b103300.txt">Table of n, a(n) for n = 0..198</a>
%H Peter Luschny, <a href="http://luschny.de/math/rulers/rulercnt.html">Perfect and Optimal Rulers.
%H Arch D. Robison, <a href="http://software.intel.com/articles/parallelcomputationofsparserulers">Parallel Computation of Sparse Rulers</a>, Jan 14 2014.
%H <a href="/index/Per#perul">Index entries for sequences related to perfect rulers.</a>
%F a(n) = T(n, A103298(n)) where the triangle T is described by A103294.
%e a(5)=4 counts the perfect rulers with length 5, {[0,1,3,5],[0,2,4,5],[0,1,2,5],[0,3,4,5]}.
%Y Cf. A004137 (Maximal number of edges in a graceful graph on n nodes).
%Y Cf. A103301, A103297, A103298.
%K nonn,nice
%O 0,4
%A _Peter Luschny_ Feb 28 2005
