9999900000domain: NAppears in sequencesa(n) = 10^n - n^5.at n=10A024119Numbers k such that k*(k+2) gives the concatenation of two numbers m and m-2.at n=10A116273a(n) = 100^n - 10^n.at n=5A276352Oblong (or pronic) numbers of the form x_n.y_n where z_n indicates the digit z repeated n times.at n=18A289980