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A307347
Number of 2n-move closed antelope paths on an unbounded chessboard from a given square to the same square.
4
1, 8, 168, 5120, 190120, 7939008, 357713664, 17010543264, 842994009000, 43192225007360, 2275378947981568, 122724475613935104, 6753785574641857024, 378138077830110886400, 21486835143540141873120, 1236506847203439155401920, 71934214120446285067176360
OFFSET
0,2
COMMENTS
Antelope is a leaper [3,4].
LINKS
FORMULA
a(n) = the constant term in the expansion of (x^4*y^3 + x^3*y^4 + 1/x^4*y^3 + 1/x^3*y^4 + x^4/y^3 + x^3/y^4 + 1/x^4/y^3 + 1/x^3/y^4)^(2*n).
Conjecture: a(n) ~ 64^n / (25*Pi*n).
MAPLE
b:= proc(n, x, y) option remember; `if`(max(x, y)>4*n or x+y>7*n, 0,
`if`(n=0, 1, add(b(n-1, abs(x+l[1]), abs(y+l[2])), l=[[4, 3],
[3, 4], [-4, 3], [-3, 4], [4, -3], [3, -4], [-4, -3], [-3, -4]])))
end:
a:= n-> b(2*n, 0$2):
seq(a(n), n=0..25);
# second Maple program:
poly := expand((x^4*y^3 + x^3*y^4 + 1/x^4*y^3 + 1/x^3*y^4 + x^4/y^3 + x^3/y^4 + 1/x^4/y^3 + 1/x^3/y^4)^2): z:=1: for n to 100 do z:=expand(z*poly): print(n, coeff(coeff(z, x, 0), y, 0)); end do:
MATHEMATICA
poly = Expand[(x^4*y^3 + x^3*y^4 + 1/x^4*y^3 + 1/x^3*y^4 + x^4/y^3 + x^3/y^4 + 1/x^4/y^3 + 1/x^3/y^4)^2]; z = 1; Flatten[{1, Table[z = Expand[z*poly]; z[[1]], {n, 1, 15}]}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Apr 03 2019
STATUS
approved