cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-6 of 6 results.

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.

Original entry on oeis.org

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
Offset: 1

Views

Author

Alois P. Heinz, Nov 26 2010

Keywords

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

Examples

			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,  ...
		

Crossrefs

Rows n=1-2 give: A000027, A006235.
Main diagonal gives A252767.
Cf. A156308.

Programs

  • 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-François Alcover, Dec 05 2013, after N. J. A. Sloane *)

Formula

A(n,k) = 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 equals k times the resultant (R(k,x), U(n-1,(2 - x)/2)). - Peter Bala, May 01 2014 [Corrected by Pontus von Brömssen, Apr 08 2025]

A158880 Number of spanning trees in C_6 X P_n.

Original entry on oeis.org

6, 8100, 7741440, 7138643400, 6551815840350, 6009209192448000, 5511006731579419434, 5054037303588059379600, 4634949992739663836897280, 4250612670512943969574312500, 3898145031429828405122837863554
Offset: 1

Views

Author

Alois P. Heinz, Mar 28 2009

Keywords

Comments

A linear divisibility sequence of order 18. - Peter Bala, May 02 2014

Crossrefs

Programs

  • Maple
    a:= n-> 6* (Matrix(1,18, (i,j)-> -sign(j-10) *[0, 1, 1350, 1290240, 1189773900, 1091969306725, 1001534865408000, 918501121929903239, 842339550598009896600, 772491665456610639482880][1+abs(j-10)]). Matrix(18, (i,j)-> if i=j-1 then 1 elif j=1 then [842608511100, -639641521152, 276457068288, -65829977967, 8292106368, -524839680, 16393554, -232704, 1152, -1][1+abs(i-9)] else 0 fi)^n) [1,10]: seq(a(n), n=1..15);

Formula

See program.
a(n) = 6*U(n-1,3/2)^2*U(n-1,5/2)^2*U(n-1,3) = 6*A001906(n)^2*A004254(n)^2*A001109(n), where U(n,x) is a Chebyshev polynomial of the second kind. - Peter Bala, May 02 2014

A158898 Number of spanning trees in C_7 X P_n.

Original entry on oeis.org

7, 35287, 113742727, 347251215703, 1050773495363767, 3174564739209417463, 9588099190533549457408, 28957256518828921149989143, 87453655435340440175476698487, 264117827347202707929587420182327
Offset: 1

Views

Author

Alois P. Heinz, Mar 29 2009

Keywords

Crossrefs

7th column of A173958.

Programs

  • Maple
    a:= n-> 7* (Matrix([222727, 4031, 71, 1, 0, -1, -71, -4031]). Matrix(8, (i,j)-> if i=j-1 then 1 elif j=1 then [71, -952, 3976, -6384, 3976, -952, 71, -1][i] else 0 fi)^n)[1,5]^2: seq(a(n), n=1..15);

Formula

See program.

A174001 Number of spanning trees in C_9 X P_n.

Original entry on oeis.org

9, 632025, 23057815104, 763341471963225, 24743382596536452489, 797880028172050676793600, 25694231385152383926116001849, 827147402338052897443922764419225, 26625078176206788678765153788526329856
Offset: 1

Views

Author

Alois P. Heinz, Nov 26 2010

Keywords

Crossrefs

Programs

  • Maple
    a:= n-> 9* (Matrix([[0, 1, 265, 50616, 9209545, 1658090689, 297747101520, 53431400864569, 9586723471888105][1+abs(i)]$i=-7..8]). Matrix(16, (i, j)-> if i=j-1 then 1 elif j=1 then [[-427427424, 327381265, -146975161, 38357160, -5699687, 457655, -17736, 265, -1][1+abs(k)]$k=-7..8][i] else 0 fi)^n)[1, 8]^2: seq(a(n), n=1..20);

Formula

See program.

A174089 Number of spanning trees in C_11 X P_n.

Original entry on oeis.org

11, 10759331, 4435600730891, 1584603178322856659, 545701094921321191290251, 185861400461684004931359802019, 63080339061067311398935095930531419, 21384626538080492686675351682716886393459
Offset: 1

Views

Author

Alois P. Heinz, Nov 26 2010

Keywords

Crossrefs

Programs

  • Maple
    a:= n-> 11* (Matrix([[0, 1, 989, 635009, 379545563, 222731206721, 129986502957277, 75726985139241127, 44091461282285910613, 25667108238650778993721, 14940759758135641310394029, 8696803311384043382138568704, 5062251640287899331740697744283, 2946638531103878161891572927216367, 1715179927870529863091149494541065923, 998372029710787510889689081784904921409, 581132402632124482558541496059410958698763][1+abs(i)]*
    signum(-i)$i=-15..16]). Matrix(32, (i, j)-> if i=j-1 then 1 elif j=1 then [[-9866686348925002518, 8584218556222705486, -5646220475933195574, 2797526034931937278, -1038052511465703094, 286230180847745070, -58096997326051905, 8585065341436957, -911803001143321, 68534901051869, -3574487862001, 125866549709, -2870938929, 39687581, -297177, 989, -1] [1+abs(k)]$k=-15..16][i] else 0 fi)^n)[1, 16]^2: seq(a(n), n=1..20);

Formula

See program.

A338832 Number of spanning trees in the k_1 X ... X k_j grid graph, where (k_1 - 1, ..., k_j - 1) is the partition with Heinz number n.

Original entry on oeis.org

1, 1, 1, 4, 1, 15, 1, 384, 192, 56, 1, 31500, 1, 209, 2415, 42467328, 1, 49766400, 1, 2558976, 30305, 780, 1, 3500658000000, 100352, 2911, 8193540096000, 207746836, 1, 76752081000, 1, 20776019874734407680, 380160, 10864, 4140081, 242716067758080000000, 1
Offset: 1

Views

Author

Pontus von Brömssen, Nov 11 2020

Keywords

Comments

a(n) > 1 precisely when n is composite.

Examples

			The partition (2, 2, 1) has Heinz number 18 and the 3 X 3 X 2 grid graph has a(18) = 49766400 spanning trees.
		

Crossrefs

2 X n grid: A001353(n) = a(2*prime(n-1))
3 X n grid: A006238(n) = a(3*prime(n-1))
4 X n grid: A003696(n) = a(5*prime(n-1))
5 X n grid: A003779(n) = a(7*prime(n-1))
6 X n grid: A139400(n) = a(11*prime(n-1))
7 X n grid: A334002(n) = a(13*prime(n-1))
8 X n grid: A334003(n) = a(17*prime(n-1))
9 X n grid: A334004(n) = a(19*prime(n-1))
10 X n grid: A334005(n) = a(23*prime(n-1))
n X n grid: A007341(n) = a(prime(n-1)^2)
m X n grid: A116469(m,n) = a(prime(m-1)*prime(n-1))
2 X 2 X n grid: A003753(n) = a(4*prime(n-1))
2 X n X n grid: A067518(n) = a(2*prime(n-1)^2)
n X n X n grid: A071763(n) = a(prime(n-1)^3)
2 X ... X 2 grid: A006237(n) = a(2^n)

Formula

a(n) = Product_{n_1=0..k_1-1, ..., n_j=0..k_j-1; not all n_i=0} Sum_{i=1..j} (2*(1 - cos(n_i*Pi/k_i))) / Product_{i=1..j} k_i, where (k_1 - 1, ..., k_j - 1) is the partition with Heinz number n.
Showing 1-6 of 6 results.