OFFSET
0,2
COMMENTS
a(n) is the number of words of length n over the alphabet {1,2,...,9} where at least one letter >= 3 appears. - Joerg Arndt, Jan 18 2024
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..300
Index entries for linear recurrences with constant coefficients, signature (11,-18).
FORMULA
a(n) = 11*a(n-1) - 18*a(n-2).
G.f.: 7*x/((1-2*x)*(1-9*x)). - Vincenzo Librandi, Oct 04 2014
a(n) = 7*A016133(n-1). - R. J. Mathar, Mar 10 2022
MATHEMATICA
Table[9^n-2^n, {n, 0, 20}] (* Harvey P. Dale, Apr 16 2014 *)
PROG
(PARI) a(n)=9^n-1<<n \\ Charles R Greathouse IV, Jun 08 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Jun 03 2011
STATUS
approved