121212

Appears in sequences

• Two-bell analog of A028355.at n=8A028359
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,2.at n=5A037487
• Periodic points under the map A053392 that adds consecutive pairs of digits and concatenates them.at n=33A053393
• Numbers that are divisible by all of their 1 and 2 digit substrings.at n=38A063527
• Triplets: base 10 representation is the juxtaposition of three identical strings.at n=11A074842
• Smallest multiple of the n-th prime beginning and ending in n with a(1)=a(3)=0.at n=11A078212
• a(n) = smallest multiple of the n-th prime whose decimal expansion is nnn...n, or 0 if no such number exists.at n=11A078251
• Smallest multiple of n using all digits of (n-1) with the same frequency and no others; or 0 if no such number exists.at n=12A083959
• Gives the i-th coefficient M(k,i) of the decomposition of the polynomials B(k,X^2) in the basis of all B(i,X), where B(i,X) is the i-th binomial polynomial: B(i,X) = X(X-1)...(X-i+1)/i! for any i > 0 and B(0,X) = 1 by definition.at n=31A100344
• n expressed in Fibonacci binary-like number system using only 1's and 2's.at n=31A108960
• Least multiple of n which is a repeated reverse concatenation of digits of n where n == 1, 3, 7 or 9 (mod 10).at n=8A110404
• Array by antidiagonals of all primitive Orloj clock striking sequences.at n=46A120449
• Sorted list of strings that can be obtained by starting with 12 and repeatedly doubling any substring in place.at n=25A130838
• a(n) = 4394*n - 1820.at n=27A156627
• 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=10A165300
• a(n) = a(n-1) + 12*100^(n-1), with a(0)=0.at n=3A177090
• List of imprimitive words over the alphabet {1,2}.at n=13A213972
• List of words over {1,2} with equal numbers of 1's and 2's.at n=13A214218
• Reversed shortest (x+1,2x)-code of n.at n=14A233137
• Non-primitive words on {1,2,3}.at n=22A239018