221121

Appears in sequences

• Successive generations of the variant of the Kolakoski sequence described in A042942.at n=3A054349
• Number of ways writing 2^n as a sum of two nonprime numbers.at n=18A062306
• Numbers k such that sigma(k) = phi(k+1) + phi(k) + phi(k-1).at n=30A065986
• a(n) is the reverse concatenation of divisors of n.at n=21A176558
• a(n) = A176558(A175354(n)) = numbers m as reverse concatenations of divisors of numbers from A175354, where A175354 = numbers k such that reverse concatenations of divisors of k are nonprimes.at n=16A176588
• List of words over {1,2} with equal numbers of 1's and 2's.at n=25A214218
• Unique representation of nonnegative numbers by iterated tribonacci A, B and C sequences.at n=49A316713
• List of co-Lyndon words on {1,2} sorted first by length and then lexicographically.at n=17A329318
• The word 1 belongs to the sequence, and whenever a word w belongs to the sequence, then the words consisting of 1's and 2's whose run lengths transform equals w also belong to the sequence.at n=27A376637