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A173958 Number A(n,k) of spanning trees in C_k X P_n; square array A(n,k), n>=1, k>=1, read by antidiagonals. 12
1, 2, 1, 3, 12, 1, 4, 75, 70, 1, 5, 384, 1728, 408, 1, 6, 1805, 31500, 39675, 2378, 1, 7, 8100, 508805, 2558976, 910803, 13860, 1, 8, 35287, 7741440, 140503005, 207746836, 20908800, 80782, 1, 9, 150528, 113742727, 7138643400, 38720000000, 16864848000, 479991603, 470832, 1 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Every row and every column of the array is a divisibility sequence, i.e., the terms satisfy the property that if n divides m then a(n) divides a(m) provided a(n) > 0. This follows from the representation of the elements of the array as a resultant. - Peter Bala, May 01 2014

LINKS

Alois P. Heinz, Antidiagonals n = 1..45, flattened

Germain Kreweras, Complexite et circuits Euleriens dans les sommes tensorielles de graphes, J. Combin. Theory, B 24 (1978), 202-212. See p. 210. - From N. J. A. Sloane, May 27 2012

Eric Weisstein's World of Mathematics, Cycle Graph

Eric Weisstein's World of Mathematics, Path Graph

Wikipedia, Kirchhoff's theorem

FORMULA

m*Prod(Prod( 4*sin(h*Pi/m)^2+4*sin(k*Pi/(2*n))^2, h=1..m-1), k=1..n-1) [Kreweras]. - From N. J. A. Sloane, May 27 2012

Let T(n,x) and U(n,x) denote the Chebyshev polynomials of the first and second kind respectively. Let R(n,x) = 2*( T(n,(x + 2)/2) - 1 )/x (the row polynomials of A156308). Then the (n,k)-th element of the array = resultant (R(k,x), U(n-1,(2 - x)/2). - Peter Bala, May 01 2014

EXAMPLE

Square array A(n,k) begins:

  1,    2,      3,         4,           5,  ...

  1,   12,     75,       384,        1805,  ...

  1,   70,   1728,     31500,      508805,  ...

  1,  408,  39675,   2558976,   140503005,  ...

  1, 2378, 910803, 207746836, 38720000000,  ...

MAPLE

with(LinearAlgebra):

A:= proc(n, m) local M, i, j;

     if m=1 then 1 else

      M:= Matrix(n*m, shape=symmetric);

      for i to n do

        for j to m-1 do M[m*(i-1)+j, m*(i-1)+j+1]:=-1 od;

        M[m*(i-1)+1, m*i]:= M[m*(i-1)+1, m*i]-1

      od;

      for i to n-1 do

        for j to m do M[m*(i-1)+j, m*i+j]:=-1 od

      od;

      for i to n*m do

        M[i, i]:= -add(M[i, j], j=1..n*m)

      od;

      Determinant(DeleteColumn(DeleteRow(M, 1), 1))

     fi

    end:

seq(seq(A(n, 1+d-n), n=1..d), d=1..9);

# Crude Maple program from N. J. A. Sloane, May 27 2012:

Digits:=200;

T:=(m, n)->round(Re(evalf(simplify(expand(

m*mul(mul( 4*sin(h*Pi/m)^2+4*sin(k*Pi/(2*n))^2, h=1..m-1), k=1..n-1))))));

# Alternative program using the resultant:

for n from 1 to 10 do seq(k*resultant(simplify((2*(ChebyshevT(k, (x + 2)/2) - 1))/x), simplify(ChebyshevU(n-1, 1 - x/2)), x), k = 1 .. 10) end do; # Peter Bala, May 01 2014

MATHEMATICA

t[m_, n_] := m*Product[Product[4*Sin[h*Pi/m]^2 + 4*Sin[k*Pi/(2*n)]^2, {h, 1, m-1}], {k, 1, n-1}]; Table[t[m, n-m+1] // Round, {n, 1, 9}, {m, n, 1, -1}] // Flatten (* Jean-Fran├žois Alcover, Dec 05 2013, after N. J. A. Sloane *)

CROSSREFS

Columns k=1-11 give: A000012, A001542, A003690, A003753, A003733, A158880, A158898, A210812, A174001, A210813, A174089.

Rows n=1-2 give: A000027, A006235.

Main diagonal gives A252767.

Cf. A156308.

Sequence in context: A187111 A122050 A081323 * A175243 A168217 A329025

Adjacent sequences:  A173955 A173956 A173957 * A173959 A173960 A173961

KEYWORD

nonn,tabl

AUTHOR

Alois P. Heinz, Nov 26 2010

STATUS

approved

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Last modified December 8 18:37 EST 2019. Contains 329865 sequences. (Running on oeis4.)