21212121

Appears in sequences

• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1.at n=7A037495
• Quadruplets: base 10 representation is the juxtaposition of four identical strings.at n=20A074843
• a(n) = 7*(10^(2*n) - 1)/33.at n=3A153848
• 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=16A165300
• List of imprimitive words over the alphabet {1,2}.at n=32A213972
• Shortest (x+1,2x)-code of n.at n=30A233135
• Underline all even terms; concatenations of underlined terms and of non-underlined terms both equal the concatenation of the entire sequence. This is the lexicographically earliest such sequence without duplicate terms and with an even digit among the first two terms.at n=33A307312