Search: id:A151423
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%I A151423
%S A151423 1,3,28,355,5264,85764,1488432,27030861,507976040,9804514720,193339562208,
               3880220133244,
%T A151423 79026982569976,1629698960355600,33969388149210240,714666181953790035,
               15158444163422689080,
%U A151423 323839596100845917400,6962822068346268247200,150567286583848676406480
%N A151423 Number of walks within N^2 (the first quadrant of Z^2) starting at (0,
               0), ending on the vertical axis and consisting of 2 n steps taken 
               from {(-1, -1), (-1, 0), (-1, 1), (1, -1), (1, 1)}
%H A151423 M. Bouquet-Melou and M. Mishna, 2008. Walks with small steps in the quarter 
               plane, <a href="http://arxiv.org/abs/0810.4387">ArXiv 0810.4387</
               a>.
%t A151423 aux[i_Integer, j_Integer, n_Integer] := Which[Min[i, j, n] < 0 || Max[i, 
               j] > n, 0, n == 0, KroneckerDelta[i, j, n], True, aux[i, j, n] = 
               aux[-1 + i, -1 + j, -1 + n] + aux[-1 + i, 1 + j, -1 + n] + aux[1 
               + i, -1 + j, -1 + n] + aux[1 + i, j, -1 + n] + aux[1 + i, 1 + j, 
               -1 + n]]; Table[Sum[aux[0, k, 2 n], {k, 0, 2 n}], {n, 0, 25}]
%Y A151423 Sequence in context: A076723 A026114 A072343 this_sequence A161605 A048954 
               A086569
%Y A151423 Adjacent sequences: A151420 A151421 A151422 this_sequence A151424 A151425 
               A151426
%K A151423 nonn,walk
%O A151423 0,2
%A A151423 Manuel Kauers (manuel(AT)kauers.de), Nov 18 2008

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