21211212domain: NAppears in sequencesList of singular subwords (or factors) of the Fibonacci word A003842.at n=4A214217List of palindromic subwords (or palindromic factors) of the Kolakoski sequence (A000002).at n=15A376688a(n) is the least palindrome that has exactly n palindromic divisors other than itself and 1.at n=31A378140