OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
D. Bevan, D. Levin, P. Nugent, J. Pantone, L. Pudwell, M. Riehl and M. L. Tlachac, Pattern avoidance in forests of binary shrubs, arXiv preprint arXiv:1510:08036 [math.CO], 2015-2016.
Index entries for linear recurrences with constant coefficients, signature (6).
FORMULA
a(n+1) = 2*6^n. - Charles R Greathouse IV, Nov 12 2009
G.f.: (1-4x)/(1-6x). - Philippe Deléham, Oct 10 2011
a(n) = ((8*n-4)*a(n-1)-12*(n-2)*a(n-2))/n, a(0)=1, a(1)=2. - Sergei N. Gladkovskii, Jul 19 2012
Sum_{n>=0} 1/a(n) = 8/5. - Amiram Eldar, Jan 02 2021
From Amiram Eldar, May 08 2023: (Start)
Sum_{n>=0} (-1)^n/a(n) = 4/7.
Product_{n>=1} (1 - 1/a(n)) = A132022. (End)
MATHEMATICA
Table[EulerPhi[6^n], {n, 0, 40}]
PROG
(PARI) a(n) = eulerphi(6^n); \\ Michel Marcus, Jan 02 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Joseph Stephan Orlovsky, Nov 10 2009
STATUS
approved