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A167747
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a(n) = phi(6^n).
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5
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1, 2, 12, 72, 432, 2592, 15552, 93312, 559872, 3359232, 20155392, 120932352, 725594112, 4353564672, 26121388032, 156728328192, 940369969152, 5642219814912, 33853318889472, 203119913336832, 1218719480020992
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OFFSET
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0,2
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LINKS
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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.
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FORMULA
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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
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MATHEMATICA
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Table[EulerPhi[6^n], {n, 0, 40}]
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PROG
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(PARI) a(n) = eulerphi(6^n); \\ Michel Marcus, Jan 02 2021
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CROSSREFS
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Cf. A000010, A000400.
Sequence in context: A119921 A322276 A279154 * A018931 A062119 A181966
Adjacent sequences: A167744 A167745 A167746 * A167748 A167749 A167750
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KEYWORD
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nonn,easy
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AUTHOR
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Vladimir Joseph Stephan Orlovsky, Nov 10 2009
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STATUS
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approved
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