OFFSET
1,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..3000
Index entries for linear recurrences with constant coefficients, signature (1, 0, 1, -1).
FORMULA
a(n) = 7*floor(n/3)+(n mod 3), with offset 0 and a(0)=0. - Gary Detlefs, Mar 09 2010
From R. J. Mathar, Mar 29 2010: (Start)
G.f.: x^2*(1+x+5*x^2)/((1+x+x^2) * (x-1)^2).
a(n) = a(n-1) + a(n-3) - a(n-4) for n>4. (End)
a(n+1) = Sum_{k>=0} A030341(n,k)*b(k) with b(0)=1 and b(k)=7*3^(k-1) for k>0. - Philippe Deléham, Oct 24 2011
From Wesley Ivan Hurt, Jun 08 2016: (Start)
a(n) = (21*n-33-12*cos(2*n*Pi/3)+4*sqrt(3)*sin(2*n*Pi/3))/9.
a(3k) = 7k-5, a(3k-1) = 7k-6, a(3k-2) = 7k-7. (End)
a(n) = n + 4*floor((n-1)/3) - 1. - Bruno Berselli, Feb 06 2017
MAPLE
seq(7*floor(n/3)+(n mod 3), n=0..60); # Gary Detlefs, Mar 09 2010
MATHEMATICA
Flatten[{#, #+1, #+2}&/@(7Range[0, 20])] (* Harvey P. Dale, Mar 05 2011 *)
PROG
(Magma) [n : n in [0..150] | n mod 7 in [0..2]]; // Wesley Ivan Hurt, Jun 08 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved