100114domain: NAppears in sequencesNumbers k such that the number of primes <= k is phi(phi(k)).at n=29A063999Smallest k whose 'Reverse and Subtract' trajectory has a preperiodic part of length n.at n=22A072138Least number that requires n steps to reach 0 by repeated application of f: x -> abs(x - reverse(x)).at n=22A109891