login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A109043 a(n) = lcm(n,2). 17
0, 2, 2, 6, 4, 10, 6, 14, 8, 18, 10, 22, 12, 26, 14, 30, 16, 34, 18, 38, 20, 42, 22, 46, 24, 50, 26, 54, 28, 58, 30, 62, 32, 66, 34, 70, 36, 74, 38, 78, 40, 82, 42, 86, 44, 90, 46, 94, 48, 98, 50, 102, 52, 106, 54, 110, 56, 114, 58, 118, 60, 122, 62, 126, 64, 130, 66, 134 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

For n > 0: a(n) = A186421(n) + A186421(n+2).

Exponent of the dihedral group D(2n) = <x, y | x^n = y^2 = 1, yxy = x^-1>. - Arkadiusz Wesolowski, Sep 10 2013

Second column of table A210530. - Boris Putievskiy, Jan 29 2013

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..10000

Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).

FORMULA

a(n) = n*2 / gcd(n, 2).

a(n) = -(n*((-1)^n-3))/2. - Stephen Crowley, Feb 11 2007

From R. J. Mathar, Aug 20 2008: (Start)

a(n) = A066043(n), n > 1.

a(n) = 2*A026741(n).

G.f.: 2x(1+x+x^2)/((1-x)^2*(1+x)^2). (End)

a(n) = n*A000034(n). - Paul Curtz, Mar 25 2011

MATHEMATICA

LCM[Range[0, 70], 2] (* Harvey P. Dale, Aug 19 2012 *)

PROG

(Sage) [lcm(n, 2) for n in xrange(0, 68)] # Zerinvary Lajos, Jun 07 2009

(MAGMA) [-(n*((-1)^n-3))/2: n in [0..70]]; // Vincenzo Librandi, Aug 12 2011

(Haskell)

a109043 = (lcm 2)

a109043_list = zipWith (*) [0..] a000034_list

-- Reinhard Zumkeller, Mar 31 2012

(MAGMA) [0, 2, 2] cat [Exponent(DihedralGroup(n)) : n in [3..65]] // Arkadiusz Wesolowski, Sep 10 2013

(PARI) a(n)=lcm(n, 2) \\ Charles R Greathouse IV, Sep 24 2015

CROSSREFS

Cf. A109042, A000034, A152749 (partial sums).

Cf. A066043 (essentially the same), A000034 (=a(n)/n), A026741 (=a(n)/2).

Sequence in context: A292258 A140524 A204904 * A054585 A278236 A278226

Adjacent sequences:  A109040 A109041 A109042 * A109044 A109045 A109046

KEYWORD

nonn,easy

AUTHOR

Mitch Harris, Jun 18 2005

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 16 21:20 EDT 2019. Contains 324155 sequences. (Running on oeis4.)