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A167747 a(n) = phi(6^n). 7
1, 2, 12, 72, 432, 2592, 15552, 93312, 559872, 3359232, 20155392, 120932352, 725594112, 4353564672, 26121388032, 156728328192, 940369969152, 5642219814912, 33853318889472, 203119913336832, 1218719480020992, 7312316880125952, 43873901280755712, 263243407684534272 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
LINKS
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.
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
a(n) = A000010(A000400(n)). - Michel Marcus, 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
Sequence in context: A119921 A322276 A279154 * A018931 A062119 A181966
KEYWORD
nonn,easy
AUTHOR
STATUS
approved

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Last modified April 14 07:36 EDT 2024. Contains 371655 sequences. (Running on oeis4.)