A125058 A sequence of words over an alphabet of two letters: a(0) = 1, a(1) = 2; a(n+2) = a(n+1)a(n)a(n+1).

1, 2, 212, 2122212, 21222122122122212, 21222122122122212212221221222122122122212, 212221221221222122122212212221221221222122122212212212221221222122122122212212221221222122122122212

Offset: 0

Author

N. J. A. Sloane, Jan 10 2007

Keywords

• nonn
• base

Comments

A055642(a(n)) = A001333(n). - Reinhard Zumkeller, Feb 02 2007

References

• Suggested by a posting by Igor G. Korepanov to "Jim's Forum", Jan 10 2007.

Programs

Mathematica

nxt[{a_,b_}]:={b,FromDigits[Flatten[Join[IntegerDigits[b],IntegerDigits[a],IntegerDigits[ b]]]]}; NestList[nxt,{1,2},7][[All,1]] (* Harvey P. Dale, Jun 05 2021 *)

Formula

a(n)=(a(n-1)*A011557(A001333(n-2))+a(n-2))*A011557(A001333(n-2))+a(n-1). - Reinhard Zumkeller, Feb 02 2007