118274domain: NAppears in sequencesNumbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 27.at n=21A031615Numbers of the form h^i + k^j where h,i,j,k are distinct positive integers and max{h,i,j,k} - min{h,i,j,k} = 3.at n=40A391670