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 A005060 a(n) = 5^n - 4^n. 19
 0, 1, 9, 61, 369, 2101, 11529, 61741, 325089, 1690981, 8717049, 44633821, 227363409, 1153594261, 5835080169, 29443836301, 148292923329, 745759583941, 3745977788889, 18798608421181, 94267920012849 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Also, the number of numbers with at most n digits whose largest digit equals 4. - M. F. Hasler, May 03 2015 a(n) is divisible by 7 iff n is divisible by 6; for example: a(6) = 11529 = 7 * 1647 (see 'Les cahier du bac' or subtract A070365 and A153727 and locate zeros). - Bernard Schott, Oct 02 2020 REFERENCES Les Cahiers du Bac, Terminales C & E, Tome 1, 1985, Exercice 109, p. 18; Bac Rouen, SÃ©rie C, 1978. LINKS Muniru A Asiru, Table of n, a(n) for n = 0..200 X. Acloque, Polynexus Numbers and other mathematical wonders [broken link] Samuele Giraudo, Pluriassociative algebras I: The pluriassociative operad, arXiv:1603.01040 [math.CO], 2016. Index entries for linear recurrences with constant coefficients, signature (9,-20). FORMULA a(n) = 5*a(n-1) + 4^(n-1). - Xavier Acloque, Oct 20 2003 From Mohammad K. Azarian, Jan 14 2009: (Start) G.f.: 1/(1-5*x) - 1/(1-4*x). E.g.f.: e^(5*x) - e^(4*x). (End) a(n) = 9*a(n-1) - 20*a(n-2), a(0)=0, a(1)=1. - Vincenzo Librandi, Jan 28 2011 MAPLE a:=n->sum(4^(n-j)*binomial(n, j), j=1..n): seq(a(n), n=0..18); # Zerinvary Lajos, Jan 04 2007 MATHEMATICA a[n_]:=5^n-4^n; a[Range[0, 60]] (* Vladimir Joseph Stephan Orlovsky, Jan 27 2011 *) LinearRecurrence[{9, -20}, {0, 1}, 30] (* Harvey P. Dale, Oct 01 2016 *) PROG (Sage) [lucas_number1(n, 9, 20) for n in range(21)]  # Zerinvary Lajos, Apr 23 2009 (PARI) a(n)=5^n-4^n \\ M. F. Hasler, May 03 2015 (GAP) List([0..20], n->5^n - 4^n); # Muniru A Asiru, Mar 04 2018 CROSSREFS Sequence in context: A202120 A201084 A305783 * A125346 A190666 A016200 Adjacent sequences:  A005057 A005058 A005059 * A005061 A005062 A005063 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified May 16 17:22 EDT 2021. Contains 343949 sequences. (Running on oeis4.)