OFFSET
1,1
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (6,-11,6).
FORMULA
a(n) = (A007689(n)+1)/2.
From Colin Barker, Apr 07 2016: (Start)
a(n) = 6*a(n-1)-11*a(n-2)+6*a(n-3) for n>3.
G.f.: x*(3-11*x+9*x^2) / ((1-x)*(1-2*x)*(1-3*x)).
(End)
a(n) = A001550(n)/2, for n >= 1. - Altug Alkan, Apr 08 2016
EXAMPLE
a(3) = (1 + 2^3 + 3^3)/2 = 18.
MATHEMATICA
Table[(1 + 2^n + 3^n)/2, {n, 30}] (* Michael De Vlieger, Apr 07 2016 *)
PROG
(PARI) Vec(x*(3-11*x+9*x^2)/((1-x)*(1-2*x)*(1-3*x)) + O(x^50)) \\ Colin Barker, Apr 07 2016
(PARI) a(n) = (1 + 2^n + 3^n)/2 \\ Charles R Greathouse IV, Apr 07 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emre APARI, Apr 07 2016
STATUS
approved