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A001668
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Number of self-avoiding n-step walks on honeycomb lattice.
(Formerly M2559 N1013)
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8
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1, 3, 6, 12, 24, 48, 90, 174, 336, 648, 1218, 2328, 4416, 8388, 15780, 29892, 56268, 106200, 199350, 375504, 704304, 1323996, 2479692, 4654464, 8710212, 16328220, 30526374, 57161568, 106794084, 199788408, 372996450, 697217994, 1300954248
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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REFERENCES
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N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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mu^n <= a(n) <= mu^n alpha^sqrt(n) for mu = A179260 and some alpha. It has been conjectured that a(n) ~ mu^n * n^(11/32). - Charles R Greathouse IV, Nov 08 2013
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MAPLE
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a:= proc(n) local v, b;
if n<2 then return 1 +2*n fi;
v:= proc() false end: v(0, 0), v(1, 0):= true$2;
b:= proc(n, x, y) local c;
if v(x, y) then 0
elif n=0 then 1
else v(x, y):= true;
c:= b(n-1, x+1, y) + b(n-1, x-1, y) +
b(n-1, x, y-1+2*((x+y) mod 2));
v(x, y):= false; c
fi
end;
6*b(n-2, 1, 1)
end:
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MATHEMATICA
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a[n_] := a[n] = Module[{v, b}, If[n < 2 , Return[1+2*n]]; v[0, 0] = v[1, 0] = True; v[_, _] = False; b[m_, x_, y_] := Module[{c}, If[v[x, y], 0 , If[ m == 0 , 1, v[x, y] = True; c = b[m-1, x+1, y] + b[m-1, x-1, y] + b[m-1, x, y-1 + 2*Mod[x+y, 2]]; v[x, y] = False; c]]]; 6*b[n-2, 1, 1]]; Table[Print["a(", n, ") = ", a[n]]; a[n], {n, 0, 32}] (* Jean-François Alcover, Nov 25 2013, translated from Alois P. Heinz's Maple program *)
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CROSSREFS
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KEYWORD
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nonn,walk,nice
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AUTHOR
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EXTENSIONS
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More terms from Pab Ter (pabrlos(AT)yahoo.com), May 06 2004
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STATUS
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approved
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