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 A094061 Number of n-moves paths of a king starting and ending at the origin of an infinite chessboard. 21
 1, 0, 8, 24, 216, 1200, 8840, 58800, 423640, 3000480, 21824208, 158964960, 1171230984, 8668531872, 64574844048, 483114856224, 3630440899800, 27379154692032, 207172490054816, 1572194644061184, 11962847247681616, 91242602561647680, 697438669619791008 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS The chessboard here is the full four-quadrant board Z X Z. This is an analog of A054474 for walks on a square grid where the steps can be made diagonally as well. a(n) is the constant term in the expansion of ((x + 1/x) * (y + 1/y) + x^2 + 1/x^2 + y^2 + 1/y^2)^n. - Seiichi Manyama, Nov 03 2019 REFERENCES Joyner, D., "Adventures in Group Theory: Rubik's Cube, Merlin's Machine and Other Mathematical Toys", Johns Hopkins University Press, 2002, pp. 79 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..1000 FORMULA D-finite with recurrence (n+1)^2*a(n+1) = n*(5*n+1)*a(n) + 2*(15*n^2+6*n-5)*a(n-1) - 8*(5*n^2-23*n+21) *a(n-2) - 64*(n-2)^2*a(n-3). G.f.: (2/(Pi*(1+4*x))) * EllipticK(4*sqrt(x*(1+x))/(1+4*x)) = 1/(1+4*x) * hypergeom([1/2,1/2], [1], 16*(x*(1+x))/(1+4*x)^2). - Sergey Perepechko, Jan 15 2011 a(n) ~ 2^(3*n+1)/(3*Pi*n). - Vaclav Kotesovec, Aug 16 2013 a(n) = (1/Pi^2) * Integral_{y = 0..Pi} Integral_{x = 0..Pi} (2*cos(x) + 2*cos(y) + 4*cos(x)*cos(y))^n dx dy. - Peter Bala, Feb 14 2017 a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(n,k) * A002426(k)^2. - Seiichi Manyama, Oct 29 2019 MAPLE a:=array(0..30):a[0]:=1:a[1]:=0:a[2]:=8:a[3]:=24:for n from 3 to 29 do a[n+1]:= (n*(5*n+1)*a[n]+2*(15*n^2+6*n-5)*a[n-1]-8*(5*n^2-23*n+21)*a[n-2]-64*(n-2)^2*a[n-3])/(n+1)^2: print(n+1, a[n+1]) od: # second Maple program a:= proc(n) option remember; `if`(n<3, (n-1)*(9*n-2)/2,       ((n-1)*(3*n-1)*(3*n-4) *a(n-1)       +(108*n^3-396*n^2+452*n-152) *a(n-2)       +32*(3*n-2)*(n-2)^2 *a(n-3))/ (n^2*(3*n-5)))     end: seq(a(n), n=0..30);  # Alois P. Heinz, Nov 02 2012 MATHEMATICA a[n_]:=Module[{f=(x+x^-1+y+y^-1+x y+x^-1y+x^-1y^-1+x y^-1)^n, s}, s=Series[f, {x, 0, 0}, {y, 0, 0}]; SeriesCoefficient[s, {0, 0}]] - Armin Vollmer (Armin.Vollmer(AT)kabelleipzig.de), May 01 2006 CoefficientList[Series[1/(1+4*x)*LegendreP[-1/2, 1-32*x*(1+x)/(1+4*x)^2], {x, 0, 20}], x] (* Vaclav Kotesovec, Aug 16 2013 *) PROG (Maxima) a[0]:1\$ a[1]:0\$ a[2]:8\$ a[3]:24\$ a[n]:=((n-1)*(3*n-1)*(3*n-4) *a[n-1]       +(108*n^3-396*n^2+452*n-152) *a[n-2]       +32*(3*n-2)*(n-2)^2 *a[n-3])/ (n^2*(3*n-5))\$ A094061(n):=a[n]\$ makelist(A094061(n), n, 0, 30); /* Martin Ettl, Nov 03 2012 */ (PARI) {a(n) = sum(k=0, n, (-1)^(n-k)*binomial(n, k)*polcoef((1+x+1/x)^k, 0)^2)} \\ Seiichi Manyama, Oct 29 2019 (PARI) {a(n) = polcoef(polcoef(((x+1/x)*(y+1/y)+x^2+1/x^2+y^2+1/y^2)^n, 0), 0)} \\ Seiichi Manyama, Nov 03 2019 CROSSREFS Row 2 of A327751. Cf. A002426, A098070, A126869, A253974, A254129, A254459, A329024. Sequence in context: A226962 A221784 A052656 * A182589 A002268 A050893 Adjacent sequences:  A094058 A094059 A094060 * A094062 A094063 A094064 KEYWORD nonn,easy AUTHOR Matthijs Coster, Apr 29 2004 EXTENSIONS More terms from and entry improved by Sergey Perepechko, Sep 06 2004 STATUS approved

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Last modified August 3 19:49 EDT 2020. Contains 336201 sequences. (Running on oeis4.)