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 1-5 of 5 results.

A354741 Triangular array read by rows. T(n,k) is the number of n X n Boolean matrices with row rank k, n >= 0, 0 <= k <= n.

Original entry on oeis.org

1, 1, 1, 1, 9, 6, 1, 49, 306, 156, 1, 225, 8550, 37488, 19272, 1, 961, 194850, 4811700, 17551800, 10995120
Offset: 0

Views

Author

Geoffrey Critzer, Jun 12 2022

Keywords

Comments

Compare to A286331 which counts n X n matrices over the field GF(2). Note that the limit when n->oo of the probability that a matrix over GF(2) has rank n is equal to Product_{i>=1} (1-1/2^i) = 0.288... (see A048651). Here, it appears (from some empirical computations) that the limiting probability that a Boolean matrix has rank n is 1.

Examples

			Table begins:
  1;
  1,   1;
  1,   9,    6;
  1,  49,  306,   156;
  1, 225, 8550, 37488, 19272;
  ...
		

Crossrefs

Columns k = 0 and 1 give A000012, A060867.
Row sums give A002416.

Programs

  • Mathematica
    Table[B = Tuples[Tuples[{0, 1}, nn],nn]; bospan[matrix_]:= Sort[DeleteDuplicates[
         Map[Clip[Total[#]] &, Drop[Subsets[matrix], 1]]]]; rowrank[matrix_] :=
       If[Total[Map[Total, matrix]] == 0, 0, Length[Select[Drop[Subsets[DeleteCases[matrix, Table[0, {nn}]]], 1],
           bospan[#] == bospan[DeleteCases[matrix, Table[0, {nn}]]] &][[ 1]]]]; Tally[
        Table[rowrank[B[[i]]], {i, 1, 2^(nn^2)}]][[All,2]], {nn, 0, 4}] // Grid

Formula

T(n,0) = 1.
T(n,1) = (2^n-1)^2.
T(n,2) = (3^n - 2*2^n + 1)^2 + (1/2)*(4^n - 2*3^n + 2^n)^2.

Extensions

Row n=5 from Pontus von Brömssen, Jul 14 2022

A355333 Triangle read by rows: T(n,k) is the number of n X n Boolean matrices with Schein rank k, 0 <= k <= n.

Original entry on oeis.org

1, 1, 1, 1, 9, 6, 1, 49, 306, 156, 1, 225, 8550, 40656, 16104, 1, 961, 194850, 5771100, 21165720, 6421800
Offset: 0

Views

Author

Pontus von Brömssen, Jun 29 2022

Keywords

Comments

Also, T(n,k) is the number of spanning subgraphs of the complete bipartite graph K_{n,n} that have bipartite dimension (or biclique covering number) k.

Examples

			Triangle begins:
  n\k | 0   1      2       3        4       5
  ----+--------------------------------------
   0  | 1
   1  | 1   1
   2  | 1   9      6
   3  | 1  49    306     156
   4  | 1 225   8550   40656    16104
   5  | 1 961 194850 5771100 21165720 6421800
		

Crossrefs

Cf. A002416 (row sums), A064230, A286331, A354741, A355334.

A322556 The number of eigenvectors with eigenvalue 1 summed over all linear operators on the vector space GF(2)^n.

Original entry on oeis.org

0, 1, 12, 448, 61440, 32505856, 67645734912, 558551906910208, 18374686479671623680, 2413129272746388704198656, 1266412660188944021221804081152, 2657157917355198038900481496478384128, 22295300680659888126120304278929453214597120
Offset: 0

Views

Author

Geoffrey Critzer, Aug 28 2019

Keywords

Comments

Generally, for any prime power q, the total number of eigenvectors corresponding to any element lambda in the field GF(q) summed over all operators on GF(q)^n is equal to (q^n-1)*q^(n^2-n).

Crossrefs

Cf. A286331.

Programs

  • Mathematica
    Map[Total,Table[Table[(q^(n - k) - 1) Product[(q^n - q^i)^2/(q^k - q^i), {i, 0,k - 1}] /. q -> 2, {k, 0, n}], {n, 0, 11}]]

Formula

a(n) = (2^n-1)*2^(n^2-n).

A333329 Number of winnable configurations in Lights Out game (played on a digraph) summed over every labeled digraph on n nodes.

Original entry on oeis.org

1, 3, 43, 2619, 654811, 662827803, 2699483026843, 44102911693372059, 2886238576935227688091, 756075355087132847491422363, 792522435884210281153847457333403, 3323493099535510709729189614466101940379, 55754039618636998102358059592995073452269940891
Offset: 0

Views

Author

Geoffrey Critzer, Mar 15 2020

Keywords

Comments

Here a digraph may have at most one self loop (cf. A002416). A winnable configuration is a subset of lit vertices that can be turned off by some toggling sequence. In this version of the game, the digraph D is not necessarily symmetric so that the number of winnable configurations is 2^rank(A^t) where A^t is the transpose of the adjacency matrix of D.
In the limit as n goes to infinity, the probability that a random configuration on a random digraph is winnable is: Sum_{j>=0} (1/2^j) * (Product_{i>=j+1} (1-2^i))/(Product_{i>=1} (2^i - 2^(j-i))) = 0.610321...

Programs

  • Mathematica
    Table[Table[2^k*Product[(2^n - 2^i)^2 /(2^k - 2^i), {i, 0, k - 1}], {k, 0, n}] // Total, {n, 0, 12}]

Formula

a(n) = Sum_{k=0..n} A286331(n,k)*2^k.
a(n) ~ c * 2^(n*(n+1)), where c = 0.610321518048266425924048782090628564983520109965690835927574616905934... - Vaclav Kotesovec, Apr 07 2020

A379105 Triangular array read by rows. T(n,k) is the number of n X n matrices T over GF(2) such that there are exactly 2^k vectors v in GF(2)^n with Tv=v, n>=0, 0<=k<=n.

Original entry on oeis.org

1, 1, 1, 6, 9, 1, 168, 294, 49, 1, 20160, 37800, 7350, 225, 1, 9999360, 19373760, 4036200, 144150, 961, 1, 20158709760, 39687459840, 8543828160, 326932200, 2542806, 3969, 1, 163849992929280, 325139829719040, 71124337751040, 2812314375360, 23435953128, 42677334, 16129, 1
Offset: 0

Views

Author

Geoffrey Critzer, Dec 15 2024

Keywords

Comments

Sum_{k=0..n} T(n,k)*2^k = (2^(n+1)-1)*2^(n^2-n) so that as n->oo the average number of fixed points is 2.
T(n,k) is also the number of n X n matrices over GF(2) with nullity k. As n->oo, the probability that a random n X n matrix over GF(q) has nullity k is 1/|GL_k(F_q)|*Product_{i>=k+1} (1 - 1/q^i). - Geoffrey Critzer, Dec 31 2024

Examples

			Triangle T(n,k) begins:
        1;
        1,        1;
        6,        9,       1;
      168,      294,      49,      1;
    20160,    37800,    7350,    225,   1;
  9999360, 19373760, 4036200, 144150, 961, 1;
  ...
		

Crossrefs

Cf. A060867 (T(n,n-1)), A002884 (column k=0), A086699 (column k=1), A346381, A286331.
Row sums give A002416.

Programs

  • Mathematica
    nn = 5; b[p_, i_] := Count[p, i];d[p_, i_] := Sum[j b[p, j], {j, 1, i}] + i Sum[b[p, j], {j, i + 1, Total[p]}];aut[deg_, p_] :=Product[Product[q^(d[p, i] deg) - q^((d[p, i] - k) deg), {k, 1, b[p, i]}], {i, 1, Total[p]}]; \[Nu] = Table[1/n Sum[MoebiusMu[n/d] q^d, {d, Divisors[n]}], {n, 1, nn}]; L=Level[Table[IntegerPartitions[n], {n, 0, nn}], {2}]; g[u_, v_, deg_] :=  Total[Map[v^Length[#] u^(deg Total[#])/aut[deg, #] &, L]]; Map[Select[#, # > 0 &] &,  Table[Product[q^n - q^i, {i, 0, n - 1}], {n, 0,nn}] CoefficientList[Series[g[u, 1, 1] g[u, v, 1] Product[g[u, 1, deg]^\[Nu][[deg]], {deg, 2, nn}], {u, 0, nn}], {u,v}]] // Grid

Formula

T(n,k)=Product_{j=0..n-k-1} (2^n - 2^j)^2/(2^(n-k)-2^j). - Geoffrey Critzer, Dec 31 2024
Showing 1-5 of 5 results.