A328991 a(n) = concatenation of a(n-1),2,a(n-2),2,a(n-1), with a(1)=1, a(2)=1221.

1, 1221, 12212121221, 1221212122121221212212121221, 122121212212122121221212122121221212122121221212122121221212212121221

Offset: 1

Author

N. J. A. Sloane, Nov 09 2019

Keywords

• nonn

Comments

In the Allombert et al. (2018) paper the sequence starts with a(0) = the empty string.

References

• Allombert, Bill, Nicolas Brisebarre, and Alain Lasjaunias. "On a two-valued sequence and related continued fractions in power series fields." The Ramanujan Journal 45.3 (2018): 859-871. See W_n in Theorem 2.