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 A008602 Multiples of 20. 13
 0, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 520, 540, 560, 580, 600, 620, 640, 660, 680, 700, 720, 740, 760, 780, 800, 820, 840, 860, 880, 900, 920, 940, 960, 980, 1000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The multiples of 20 are exactly those integers which do not have a multiple whose decimal digits are of alternating parity. (International Mathematical Olympiad 2004, problem 6.) - Joseph Myers, Jul 13 2004 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Tanya Khovanova, Recursive Sequences INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 332 Luis Manuel Rivera, Integer sequences and k-commuting permutations, arXiv preprint arXiv:1406.3081, 2014 Index entries for linear recurrences with constant coefficients, signature (2, -1). FORMULA G.f.: 20*x/(x-1)^2. - Vincenzo Librandi, Jun 10 2013 MATHEMATICA Range[0, 1500, 20] (* Vladimir Joseph Stephan Orlovsky, Jun 01 2011 *) CoefficientList[Series[20 x / (x - 1)^2, {x, 0, 60}], x] (* Vincenzo Librandi, Jun 10 2013 *) PROG (PARI) a(n)=20*n \\ Charles R Greathouse IV, Sep 28 2015 CROSSREFS Cf. A008600, A008601. Sequence in context: A104153 A049057 A065607 * A061830 A235282 A270296 Adjacent sequences:  A008599 A008600 A008601 * A008603 A008604 A008605 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified November 19 19:37 EST 2018. Contains 317364 sequences. (Running on oeis4.)