OFFSET
0,1
COMMENTS
Row sums of (8, 1)-Pascal triangle A093565. - N. J. A. Sloane, Sep 22 2004
The first differences are the sequence itself. - Alexandre Wajnberg & Eric Angelini, Sep 07 2005
For n>=1, a(n) is equal to the number of functions f:{1,2,...,n+2}->{1,2,3} such that for fixed, different x_1, x_2,...,x_n in {1,2,...,n+2} and fixed y_1, y_2,...,y_n in {1,2,3} we have f(x_i)<>y_i, (i=1,2,...,n). - Milan Janjic, May 10 2007
9 times powers of 2. - Omar E. Pol, Dec 16 2008
a(n) = A173786(n+3,n) for n>2. - Reinhard Zumkeller, Feb 28 2010
Let D(m) = {d(m,i)}, i = 1..q, denote the set of the q divisors of a number m, and consider s0(m) and s1(m) the sums of the divisors that are congruent to 2 and 3 (mod 4) respectively. For n>0, the sequence a(n) lists the numbers m such that s0(m) = 26 and s1(m) = 3. - Michel Lagneau, Feb 10 2017
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..235
Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
Tanya Khovanova, Recursive Sequences
Index entries for linear recurrences with constant coefficients, signature (2).
FORMULA
a(n) = 9*2^n.
G.f.: 9/(1-2*x).
a(n) = A118416(n+1,5) for n>4. - Reinhard Zumkeller, Apr 27 2006
a(n) = 2*a(n-1), n>0; a(0)=9. - Philippe Deléham, Nov 23 2008
a(n) = 9*A000079(n). - Omar E. Pol, Dec 16 2008
a(n) = 3*A007283(n). - Omar E. Pol, Jul 14 2015
E.g.f.: 9*exp(2*x). - Elmo R. Oliveira, Aug 16 2024
MATHEMATICA
9*2^Range[0, 60] (* Vladimir Joseph Stephan Orlovsky, Jun 09 2011 *)
PROG
(Magma) [9*2^n: n in [0..40]]; // Vincenzo Librandi, Apr 28 2011
(PARI) a(n)=9<<n \\ Charles R Greathouse IV, Apr 17 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jun 14 1998
STATUS
approved