This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A121389 #7 Dec 24 2022 11:48:05 %S A121389 0,9,9,99,999,99999,99999999,9999999999999,999999999999999999999, %T A121389 9999999999999999999999999999999999, %U A121389 9999999999999999999999999999999999999999999999999999999 %N A121389 a(n) = 10^Fibonacci(n) - 1. %C A121389 Each a(n) has Fibonacci(n) (trailing) 9's. In general, if the same recurrence below is used with any a(0), a(1) >= 0, then, for all k >= 2, a(k) has the same number of trailing 9's as a(k-2) and a(k-1) have altogether (see for example A121390). %F A121389 a(n) = 10^Fibonacci(n) - 1 = 10^A000045(n) - 1 (= 9*A108047(n) for n>=1). a(0) = 0; a(1) = 9; a(n) = a(n-2)*a(n-1) + a(n-2) + a(n-1). %t A121389 10^Fibonacci[Range[0,10]]-1 (* _Harvey P. Dale_, Dec 24 2022 *) %Y A121389 Cf. A000045, A063896, A108047, A121390. %K A121389 nonn %O A121389 0,2 %A A121389 _Rick L. Shepherd_, Jul 26 2006