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A008602 Multiples of 20. 17
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 [math.CO], 2014-2015.

Index entries for linear recurrences with constant coefficients, signature (2,-1).

FORMULA

G.f.: 20*x/(x - 1)^2. - Vincenzo Librandi, Jun 10 2013

E.g.f.: 20*x*exp(x). - Stefano Spezia, Feb 20 2020

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

(Scala) (0 to 1000 by 20).toList // Alonso del Arte, Feb 20 2020

CROSSREFS

Cf. A008600, A008601, A215145.

Sequence in context: A104153 A049057 A065607 * A061830 A235282 A270296

Adjacent sequences:  A008599 A008600 A008601 * A008603 A008604 A008605

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified July 9 09:23 EDT 2020. Contains 335542 sequences. (Running on oeis4.)