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A255656 Number of length n+4 0..3 arrays with at most two downsteps in every 4 consecutive neighbor pairs.

%I A255656 #7 Jul 23 2025 15:08:49
%S A255656 968,3692,14192,54560,209412,803246,3083292,11835664,45429680,
%T A255656 174365744,669261344,2568836929,9859943512,37845226102,145260624176,
%U A255656 557551963747,2140043779888,8214097736920,31528047115872,121013635650740
%N A255656 Number of length n+4 0..3 arrays with at most two downsteps in every 4 consecutive neighbor pairs.
%C A255656 Column 4 of A255660
%H A255656 R. H. Hardin, <a href="/A255656/b255656.txt">Table of n, a(n) for n = 1..210</a>
%F A255656 Empirical: a(n) = 4*a(n-1) -4*a(n-3) +15*a(n-4) -24*a(n-5) -68*a(n-6) +136*a(n-7) -81*a(n-8) +40*a(n-9) -10*a(n-10) +4*a(n-11) -a(n-12)
%e A255656 Some solutions for n=4
%e A255656 ..3....2....1....1....2....0....2....1....0....3....3....1....1....3....2....2
%e A255656 ..0....1....3....2....1....3....2....3....2....0....1....3....0....0....2....1
%e A255656 ..1....2....0....2....3....1....1....3....0....0....1....3....1....0....0....1
%e A255656 ..1....2....2....1....3....1....3....1....1....1....2....1....1....0....1....3
%e A255656 ..2....0....3....3....0....1....0....1....3....1....3....2....2....0....3....0
%e A255656 ..2....3....1....3....2....2....3....1....3....1....3....1....2....1....1....0
%e A255656 ..0....3....1....2....1....1....3....2....3....0....1....2....2....2....0....3
%e A255656 ..0....1....2....0....3....1....0....3....0....0....1....1....1....3....1....2
%Y A255656 Cf. A255660
%K A255656 nonn
%O A255656 1,1
%A A255656 _R. H. Hardin_, Mar 01 2015