%I A005562 M3974
%S A005562 1,5,35,140,720,2700,12375,45375,196625,715715,3006003,10930920,
%T A005562 45048640,164105760,668144880,2441298600,9859090500,36149998500
%N A005562 Number of walks on square lattice.
%D A005562 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A005562 R. K. Guy, Catwalks, Sandsteps and Pascal Pyramids, <a href="http://www.cs.uwaterloo.ca/
               journals/JIS/index.html">J. Integer Seqs., Vol. 3 (2000), #00.1.6</
               a>
%F A005562 a(n) = C(n+5, ceil(n/2))*C(n+4, floor(n/2)) - C(n+5, ceil((n-1)/2))*C(n+4, 
               floor((n-1)/2)). - Paul D. Hanna (pauldhanna(AT)juno.com), Apr 16 
               2004
%o A005562 (PARI) {a(n)=binomial(n+5,ceil(n/2))*binomial(n+4,floor(n/2)) - binomial(n+5,
               ceil((n-1)/2))*binomial(n+4,floor((n-1)/2))}
%Y A005562 Cf. A005558-A005561, A093768.
%Y A005562 Sequence in context: A096743 A026697 A000910 this_sequence A097872 A124793 
               A048515
%Y A005562 Adjacent sequences: A005559 A005560 A005561 this_sequence A005563 A005564 
               A005565
%K A005562 nonn
%O A005562 4,2
%A A005562 N. J. A. Sloane (njas(AT)research.att.com).