168961domain: NAppears in sequencesa(1) = 2, a(n+1) is the largest squarefree number < 2*a(n).at n=18A076994Number of 2 X 2 matrices having all terms in {1,...,n} and even determinant.at n=22A211064Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and even determinant.at n=11A211154