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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 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 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 Cf. A000010, A000400, A132022. 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 April 14 07:36 EDT 2024. Contains 371655 sequences. (Running on oeis4.)