OFFSET
1,4
COMMENTS
A square array of n X n pixels can have two states (gray, red). Touching a pixel switches its state and the state of the adjacent pixels. The general problem is to turn all pixels ON given any initial configuration. It requires inverting a n^2 by n^2 matrix in Z/2Z. The sequence is the rank deficiency (corank) of the matrix, such that the zero terms correspond to the sizes for which the general case admits a solution.
The size 5 game can be played at the link given below. Rank deficiency is 2 for that game, but only initial configurations that admit a solution are given.
a(n) is even and satisfies a(n) <= n. - Thomas Buchholz, May 19 2014
For all indices n and natural numbers k, a(n*k - 1) >= a(n - 1). - William Boyles, Jun 17 2022
REFERENCES
See A075462 for references.
LINKS
William Boyles, Table of n, a(n) for n = 1..25000 (first 1000 terms by Max Alekseyev and Thomas Buchholz).
Andries E. Brouwer, Lights Out and Button Madness Games [Gives theory and a(n) for n = 1..1000, Jun 19 2008]
JeuxT45, Turn it red [Dead link]
Martin Kreh, "Lights Out" and Variants, The American Mathematical Monthly 124:10 (2017), 937-950.
Eric Weisstein's World of Mathematics, Lights Out Puzzle
FORMULA
Let f(k,x) = U(k,x/2), where U(k,x) is the k-th Chebyshev polynomial of the second kind over the field GF(2). So f(0,x)=1, f(1,x)=x, f(2,x)=(1+x)^2, and f(n+1,x)=x*f(n,x)+f(n-1,x). Then a(n) equals the degree of gcd(f(n,x), f(n,1+x)). For example, f(5,x)=x^5+x=x(1+x)^4 and f(5, 1+x)=x^4(1+x). So their GCD is x(1+x) and the degree is 2, that is a(5)=2. - Zhao Hui Du, Mar 17 2014; edited by Max Alekseyev, Nov 12 2019
EXAMPLE
For n=2, matrix is [1 1 1 0][1 1 0 1][1 0 1 1][0 1 1 1] which is of full rank.
MATHEMATICA
Table[First[Dimensions[NullSpace[AdjacencyMatrix[GridGraph[{n, n}]] + IdentityMatrix[n*n], Modulus -> 2]]], {n, 2, 30}]
(* Or Faster *)
A[k_] := DiagonalMatrix[Array[1 &, k - 1], -1] +
DiagonalMatrix[Array[1 &, k - 1], 1] + IdentityMatrix[k];
B[k_, 0] := IdentityMatrix[k];
B[k_, 1] := A[k];
B[k_, n_] := B[k, n] = Mod[A[k].B[k, n - 1] + B[k, n - 2], 2];
Table[First[Dimensions[NullSpace[B[n, n], Modulus -> 2]]], {n, 2, 30}]
(* Birkas Gyorgy, Jun 10 2011 *)
PROG
(PARI) { A159257(n) = my(p, q, r); p=Mod(1, 2); q=p*x; for(u=2, n, r=x*q+p; p=q; q=r); p=subst(q, x, 1+x); r=gcd(p, q); poldegree(r) } \\ Zhao Hui Du, Mar 18 2014
(PARI) { A159257(n) = my(f = polchebyshev(n, 2, x/2)*Mod(1, 2)); poldegree( gcd(f, subst(f, x, 1+x)) ); } \\ Max Alekseyev, Nov 12 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Bruno Vallet (bruno.vallet(AT)gmail.com), Apr 07 2009
EXTENSIONS
More terms from Max Alekseyev, Sep 17 2009
More terms from Thomas Buchholz, May 16 2014
STATUS
approved