252840domain: NAppears in sequencesNumber of 2 X 2 matrices with all elements in {0,1,...,n} and odd determinant.at n=28A210370Number of 2 X 2 matrices having all terms in {-n,...,0,..,n} and odd determinant.at n=14A211155Hemi-imperfect numbers: numbers such that the denominator of k/A206369(k) is equal to 2.at n=13A295236