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%I #4 Mar 01 2015 12:03:46
%S 1024,4096,16128,54560,155144,385738,864924,1788660,3467296,6376160,
%T 11223728,19042353,31307660,50094036,78275176,119780409,179919544,
%U 265791268,386792720,555250782,787198896,1103326862,1530135124
%N Number of length n+4 0..3 arrays with at most two downsteps in every n consecutive neighbor pairs
%C Row 4 of A255660
%H R. H. Hardin, <a href="/A255664/b255664.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = (1/39916800)*n^11 + (1/362880)*n^10 + (11/80640)*n^9 + (461/120960)*n^8 + (141551/1209600)*n^7 + (36127/17280)*n^6 + (14049449/725760)*n^5 + (18041057/362880)*n^4 + (35402863/302400)*n^3 + (1423187/10080)*n^2 + (1020871/3080)*n + 163 for n>2
%e Some solutions for n=4
%e ..2....2....0....1....2....1....3....2....3....3....2....3....0....1....0....3
%e ..2....3....1....0....1....0....0....0....1....2....1....1....0....3....2....3
%e ..2....0....0....1....0....0....3....1....1....0....0....2....3....1....3....3
%e ..3....1....2....2....2....2....0....0....1....0....0....1....0....0....2....2
%e ..3....0....2....1....3....1....3....0....2....1....1....2....0....0....1....0
%e ..0....1....2....0....0....3....0....2....1....2....0....3....0....3....2....1
%e ..3....1....2....0....3....0....1....3....0....0....2....2....1....1....3....3
%e ..1....1....3....3....2....0....1....2....3....1....2....2....0....1....0....2
%Y Cf. A255660
%K nonn
%O 1,1
%A _R. H. Hardin_, Mar 01 2015
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