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.

Previous Showing 11-14 of 14 results.

A289196 Number of connected dominating sets in the n X n rook graph.

Original entry on oeis.org

1, 9, 325, 51465, 30331861, 66273667449, 556170787050565, 18374555799096912585, 2414861959450912233421141, 1267166974391002542218440851129, 2658149210218078451926703769353958085, 22299979556058598891936157095746389850916425
Offset: 1

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Author

Eric W. Weisstein, Jun 28 2017

Keywords

Comments

A set of vertices in the n X n rook graph can be represented as a n X n binary matrix. The vertex set will be dominating if either every row contains a 1 or every column contains a 1. - Andrew Howroyd, Jul 18 2017

Crossrefs

Main diagonal of A360875.

Programs

  • Mathematica
    (* b = A183109, T = A262307 *) b[m_, n_] := Sum[(-1)^j*Binomial[m, j]*(2^(m - j) - 1)^n, {j, 0, m}]; T[, 1] = T[1, ] = 1; T[m_, n_] := T[m, n] = b[m, n] - Sum[T[i, j]*b[m-i, n-j]*Binomial[m-1, i-1]*Binomial[n, j], {i, 1, m-1}, {j, 1, n-1}]; a[n_] := T[n, n] + 2*Sum[ Binomial[n, k]*T[n, k], {k, 1, n-1}]; Array[a, 12] (* Jean-François Alcover, Oct 02 2017, after Andrew Howroyd *)
  • PARI
    G(N)={S=matrix(N, N); T=matrix(N, N); U=matrix(N, N);
    \\ S is A183109, T is A262307, U is m X n variant of this sequence.
    for(m=1, N, for(n=1, N,
    S[m, n]=sum(j=0, m, (-1)^j*binomial(m, j)*(2^(m - j) - 1)^n);
    T[m, n]=S[m, n]-sum(i=1, m-1, sum(j=1, n-1, T[i, j]*S[m-i, n-j]*binomial(m-1, i-1)*binomial(n, j)));
    U[m, n]=sum(i=1, m, binomial(m, i)*T[i, n])+sum(j=1, n, binomial(n,j)*T[m, j])-T[m,n] )); U}
    a(n)=G(n)[n, n]; \\ Andrew Howroyd, Jul 18 2017

Formula

a(n) = A262307(n,n) + 2*Sum_{k=1..n-1} binomial(n,k) * A262307(n,k). - Andrew Howroyd, Jul 18 2017

Extensions

Terms a(6) and beyond from Andrew Howroyd, Jul 18 2017

A297008 Number of edge covers in the complete tripartite graph K_{n,n,n}.

Original entry on oeis.org

4, 2902, 117207580, 268752741193822, 37231937318464496521924, 323097476641999571450657507823382, 178177528846515370073473806783721111760309500, 6274803675843247716007930604166972482973014660984656159102
Offset: 1

Views

Author

Eric W. Weisstein, Dec 23 2017

Keywords

Crossrefs

Programs

  • Mathematica
    b[m_, n_] := Sum[(-1)^j*Binomial[m, j]*If[n == 0, 1, (2^(m - j) - 1)^n], {j, 0, m}];
    c[n_, s_] := Sum[Binomial[n, k]*Binomial[n, s - k]*b[k, s - k], {k, Max[0, s - n], Min[n, s]}];
    a[n_] := Sum[c[n, 2*n - i]*Sum[(-1)^j*Binomial[i, j]*(2^(2*n - j) - 1)^n, {j, 0, i}], {i, 0, 2 n}];
    Array[a, 10] (* Jean-François Alcover, Dec 27 2017, after Andrew Howroyd *)
  • PARI
    \\ here b(m,n) is A183109.
    b(m, n)={sum(j=0, m, (-1)^j*binomial(m, j)*(2^(m - j) - 1)^n)}
    c(n, s)={sum(k=max(0, s-n), min(n, s),binomial(n, k)*binomial(n, s-k)*b(k, s-k))}
    a(n)={sum(i=0, 2*n, c(n, 2*n-i)*sum(j=0, i, (-1)^j*binomial(i, j)*(2^(2*n - j) - 1)^n))} \\ Andrew Howroyd, Dec 24 2017

Extensions

Terms a(4) and beyond from Andrew Howroyd, Dec 24 2017

A225783 Triangle read by rows: T(n,m) is the number of n X m binary (0,1) matrices that represent perfect parity patterns.

Original entry on oeis.org

0, 1, 0, 0, 2, 0, 0, 0, 0, 15, 0, 0, 4, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 63, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 240, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 112, 0, 0, 0, 36, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 63, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 15, 0, 0, 0, 0, 0, 0
Offset: 1

Views

Author

R. J. Mathar, Jun 13 2014

Keywords

Comments

An n X m matrix of zeros and ones is perfect if no row or column consists entirely of zeros (as counted in A183109). It is a parity pattern if every 0 is adjacent (vertically or horizontally) to an even number of 1s and every 1 is adjacent to an odd number of 1s.

Examples

			The T(5,3) = 4 perfect parity 5 X 3 patterns are
0 0 1
0 1 1
1 0 1
1 1 0
1 0 0
------
0 1 1
1 0 0
1 0 1
0 0 1
1 1 0
--------
1 0 0
1 1 0
1 0 1
0 1 1
0 0 1
--------
1 1 0
0 0 1
1 0 1
1 0 0
0 1 1
		

A283654 Triangle T(n,m) read by rows: number of n X m binary matrices with no rows or columns in which all entries are the same (n >= 1, 1 <= m <= n).

Original entry on oeis.org

0, 0, 2, 0, 6, 102, 0, 14, 906, 22874, 0, 30, 6510, 417810, 17633670, 0, 62, 42666, 6644714, 622433730, 46959933962, 0, 126, 267582, 99044946, 20218802310, 3204360965106, 451575174961302, 0, 254, 1641786, 1430529674, 630917888610, 208308918928634, 60134626974122946, 16271255119687320314
Offset: 1

Views

Author

Robert FERREOL, Mar 14 2017

Keywords

Examples

			The T(2,3)=6 matrices are
1 0 1
0 1 0
and the matrices obtained by permutations of rows and columns.
First values in triangle
0;
0, 2;
0, 6, 102;
0, 14, 906, 22874;
0, 30, 6510, 417810, 17633670;
0, 62, 42666, 6644714, 622433730, 46959933962;
0, 126, 267582, 99044946, 20218802310, 3204360965106, 451575174961302;
		

Crossrefs

Diagonal gives A283624.
Cf. A183109.

Programs

  • Maple
    T0:=(n,m)->add((-1)^(m+k)*binomial(n,k)*(2^k-1)^m, k=0..n):
    T:=(n,m)->2*T0(n,m)+2^(n*m)+(2^n-2)^m+(2^m-2)^n-2*(2^m-1)^n-2*(2^n-1)^m:
    seq(seq(T(n,m), m=1..n),n=1..10);
  • Mathematica
    T[n_, m_] := Sum[(-1)^j*Binomial[m, j]*(2^(m - j) - 1)^n, {j, 0, m}]; Flatten[Table[2*T[n, m] + 2^(n*m) + (2^n - 2)^m + (2^m - 2)^n - 2*(2^m - 1)^n - 2*(2^n - 1)^m, {n, 10}, {m, n}]] (* Indranil Ghosh, Mar 14 2017 *)
  • PARI
    T(n, m) = sum(j=0, m, (-1)^j*binomial(m, j)*(2^(m - j) - 1)^n);
    tabl(nn) = {for(n=1, nn, for(m=1, n, print1(2*T(n,m) + 2^(n*m) + (2^n - 2)^m + (2^m - 2)^n - 2*(2^m - 1)^n - 2*(2^n - 1)^m,", ");); print(););};
    tabl(10); \\ Indranil Ghosh, Mar 14 2017
    
  • Python
    import math
    f=math.factorial
    def C(n,r): return f(n)//f(r)//f(n - r)
    def T(n,m): return sum([(-1)**j*C(m,j)*(2**(m - j) - 1)**n for j in range (0, m+1)])
    i=1
    for n in range(1,11):
        for m in range(1, n+1):
            print(str(i)+" "+str(2*T(n, m) + 2**(n*m) + (2**n - 2)**m + (2**m - 2)**n - 2*(2**m - 1)**n - 2*(2**n - 1)**m))
            i+=1 # Indranil Ghosh, Mar 14 2017

Formula

T(n,m) = T(m,n) = 2*A183109(n,m) + 2^(n*m) + (2^n-2)^m + (2^m-2)^n - 2*(2^m-1)^n - 2*(2^n-1)^m.
T(n,1)=0, T(n,2)=2^n-2, T(n,3)=6^n-6*(3^n-2^n).
Previous Showing 11-14 of 14 results.