2121212

Appears in sequences

• Two-bell analog of A028355.at n=10A028359
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1.at n=6A037495
• Numbers n which in decimal have the form imj, where m is the middle digit, with property that j is the reversal of i, and i = m*j.at n=29A082945
• Palindromic primes in base 3 (written in base 3).at n=15A117698
• a(n) is the smallest number not already present that permits the cyclic repetition of the path 1,2 of the digits in the sequence.at n=13A165300
• Shortest (x+1,2x)-code of n.at n=29A233135
• Reversed shortest (x+1,2x)-code of n.at n=29A233137