OFFSET
0,2
COMMENTS
a(0)-a(4) computed by W. Edwin Clark, May 07 2013.
A226321 is a similar sequence which counts the real {0,1} matrices which are the square of a {0,1} matrix. - Giovanni Resta, Jun 03 2013
LINKS
Victor S. Miller, Table of n, a(n) for n = 0..30
Victor S. Miller, Counting Matrices that are Squares, arXiv:1606.09299 [math.GR], 2016.
Giovanni Resta, C program for a(k), with k <= 6.
PROG
(PARI) a(n)=#vecsort(lift(vector(2^n^2, k, matrix(n, n, i, j, bittest(k, (i-1)*n+j-1))^2*Mod(1, 2))), , 8) \\ Charles R Greathouse IV, May 07 2013
(PARI) ZM(k)=matrix(n, n, i, j, bittest(k, (i-1)*n+j-1))*Mod(1, 2)
MZ(M)=my(n=matsize(M)[1]); sum(i=1, n, sum(j=1, n, M[i, j]<<((i-1)*n+j-1)))
a(n)=#vecsort(vector(2^n^2, i, MZ(lift(ZM(i, n)^2))), , 8) \\ Charles R Greathouse IV, May 07 2013
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
N. J. A. Sloane, May 07 2013
EXTENSIONS
a(5)-a(6) from Giovanni Resta, May 08 2013
a(7)-a(30) from Victor S. Miller, May 24 2013
STATUS
approved