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 A199115 5*4^n+1. 3
 6, 21, 81, 321, 1281, 5121, 20481, 81921, 327681, 1310721, 5242881, 20971521, 83886081, 335544321, 1342177281, 5368709121, 21474836481, 85899345921, 343597383681, 1374389534721, 5497558138881, 21990232555521, 87960930222081 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS An Engel expansion of 4/5 to the base 4 as defined in A181565, with the associated series expansion 4/5 = 4/6 + 4^2/(6*21) + 4^3/(6*21*81) + 4^4/(6*21*81*321) + .... Cf. A136412 and A140660. - Peter Bala, Oct 29 2013 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (5,-4). FORMULA a(n) = 3*A136412(n). a(n) = 4*a(n-1)-3. a(n) = 5*a(n-1)-4*a(n-2). G.f.: 3*(2-3*x)/((1-x)*(1-4*x)).  - Bruno Berselli, Nov 04 2011 PROG (MAGMA) [5*4^n+1: n in [0..30]]; CROSSREFS Sequence in context: A255719 A134927 A108306 * A320649 A219596 A182251 Adjacent sequences:  A199112 A199113 A199114 * A199116 A199117 A199118 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Nov 04 2011 STATUS approved

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Last modified January 23 10:50 EST 2020. Contains 331171 sequences. (Running on oeis4.)