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A167747 a(n) = phi(6^n). 5
1, 2, 12, 72, 432, 2592, 15552, 93312, 559872, 3359232, 20155392, 120932352, 725594112, 4353564672, 26121388032, 156728328192, 940369969152, 5642219814912, 33853318889472, 203119913336832, 1218719480020992 (list; graph; refs; listen; history; text; internal format)
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.

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>=1} 1/a(n) = 8/5. - Amiram Eldar, Jan 02 2021

a(n) = A000010(A000400(n)). - Michel Marcus, Jan 02 2021

MATHEMATICA

Table[EulerPhi[6^n], {n, 0, 40}]

PROG

(PARI) a(n) = eulerphi(6^n); \\ Michel Marcus, Jan 02 2021

CROSSREFS

Cf. A000010, A000400.

Sequence in context: A119921 A322276 A279154 * A018931 A062119 A181966

Adjacent sequences:  A167744 A167745 A167746 * A167748 A167749 A167750

KEYWORD

nonn,easy

AUTHOR

Vladimir Joseph Stephan Orlovsky, Nov 10 2009

STATUS

approved

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Last modified July 26 10:35 EDT 2021. Contains 346294 sequences. (Running on oeis4.)