123333321domain: NAppears in sequencesAll possible products in increasing order of two distinct members of the unary sequence 1, 11, 111, 1111, 11111, ...given by A000042.at n=18A077488Algebraic cofactor of n-th repunit A002275(n).at n=20A204848Numbers that can be written as a product of distinct repunits.at n=22A334131