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A052207
Number of sequences {s(i): i=0..n} such that |s(i)-s(i-1)|=1, i=1..n and s(i)=0 at four values of i, one of which is i=0.
1
0, 0, 0, 0, 0, 8, 16, 40, 80, 168, 336, 672, 1344, 2640, 5280, 10296, 20592, 40040, 80080, 155584, 311168, 604656, 1209312, 2351440, 4702880, 9152528, 18305056, 35659200, 71318400, 139070880, 278141760, 542911320, 1085822640, 2121460200, 4242920400, 8297266560
OFFSET
1,6
COMMENTS
Calculation suggests that {a(2n)/8} is A002054 (shifted).
LINKS
Sean A. Irvine, Java program (github)
EXAMPLE
a(6) = 8: [0,-1,0,-1,0,-1,0], [0,-1,0,-1,0,1,0], [0,-1,0,1,0,-1,0], [0,-1,0,1,0,1,0], [0,1,0,-1,0,-1,0], [0,1,0,-1,0,1,0], [0,1,0,1,0,-1,0], [0,1,0,1,0,1,0].
MAPLE
a:= n-> max(0, (m-> 8*(d+1)*binomial(2*m+1, m-1))(iquo(n-4, 2, 'd'))):
seq(a(n), n=1..36); # Alois P. Heinz, Oct 30 2021
CROSSREFS
Cf. A002054.
Sequence in context: A269513 A024700 A108576 * A038578 A348925 A155110
KEYWORD
nonn
AUTHOR
John W. Layman, Jan 26 2000
EXTENSIONS
More terms from Sean A. Irvine, Oct 29 2021
STATUS
approved