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A167747 a(n) = phi(6^n). 3
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, Pattern avoidance in forests of binary shrubs, arXiv preprint arXiv:1510:08036, 2015

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

MATHEMATICA

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

CROSSREFS

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 January 23 13:40 EST 2020. Contains 331171 sequences. (Running on oeis4.)