A008602 - OEIS

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A008602

Multiples of 20.

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

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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, see A110303.) - 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 *)