212121212121
domain: N
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=11A037495
- a(n) = 7*(10^(2*n) - 1)/33.at n=5A153848
- 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=24A165300