OFFSET
1,1
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Apollonian Network
Index entries for linear recurrences with constant coefficients, signature (4,-3).
FORMULA
From Colin Barker, Jul 07 2017: (Start)
G.f.: x*(4 - 9*x) / ((1 - x)*(1 - 3*x)).
a(n) = (5 + 3^n) / 2.
a(n) = 4*a(n-1) - 3*a(n-2) for n>2.
(End)
a(n) = a(n-1) + 3^(n-1) for n>1. - Andrew D. Walker, Jul 07 2017
PROG
(PARI) a(n)=(3^n+5)/2 \\ Charles R Greathouse IV, Jul 07 2017
(PARI) Vec(x*(4 - 9*x) / ((1 - x)*(1 - 3*x)) + O(x^30)) \\ Colin Barker, Jul 07 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Andrew D. Walker, Jul 07 2017
STATUS
approved