OFFSET
0,2
COMMENTS
Length-n words from letters {1,2,...,7} with at least one letter greater than 3. - Joerg Arndt, Jun 02 2011
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..300
Index entries for linear recurrences with constant coefficients, signature (10,-21).
FORMULA
a(n) = 10*a(n-1) -21*a(n-2).
G.f.: 4*x/((1-3*x)*(1-7*x)). - Vincenzo Librandi, Oct 04 2014
MAPLE
MATHEMATICA
Table[7^n - 3^n, {n, 0, 25}] (* or *) CoefficientList[Series[4 x /((1 - 3 x) (1 - 7 x)), {x, 0, 30}], x] (* Vincenzo Librandi, Oct 04 2014 *)
LinearRecurrence[{10, -21}, {0, 4}, 20] (* Harvey P. Dale, Mar 30 2015 *)
PROG
(Magma) [7^n - 3^n: n in [0..30]];
(PARI) a(n)=7^n-3^n \\ Charles R Greathouse IV, Jun 02 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Jun 02 2011
STATUS
approved