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A106833 3n and 2n, alternating. 5
3, 4, 9, 8, 15, 12, 21, 16, 27, 20, 33, 24, 39, 28, 45, 32, 51, 36, 57, 40, 63, 44, 69, 48, 75, 52, 81, 56, 87, 60, 93, 64, 99, 68, 105, 72, 111, 76, 117, 80, 123, 84, 129, 88, 135, 92, 141, 96, 147, 100, 153, 104, 159, 108, 165, 112, 171, 116, 177, 120, 183 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..61.

FORMULA

a(n) = n*(2 + mod(n, 2)).

a(2n) = 6n + 3 = A016945(n). - Paul Curtz, Nov 23 2008

a(2n+1) = A008586(n+1).

G.f.: x*(3+4*x+3*x^2)/((x-1)^2*(1+x)^2). a(n)=2*a(n-2)-a(n-4). - R. J. Mathar, Apr 08 2009

a(n) = sumd(d divides n, mu(d)*sigma(2n/d)). - Benoit Cloitre, Oct 18 2009

a(n) = n*(5-(-1)^n)/2. - Wesley Ivan Hurt, May 14 2014

MATHEMATICA

Table[n(2 + Mod[n, 2]), {n, 50}]

PROG

(PARI) a(n)=sumdiv(n, d, moebius(d)*sigma(2*n/d)) \\ Benoit Cloitre, Oct 18 2009

CROSSREFS

Sequence in context: A022463 A239384 A242219 * A217578 A280616 A317099

Adjacent sequences:  A106830 A106831 A106832 * A106834 A106835 A106836

KEYWORD

nonn,easy

AUTHOR

Zak Seidov, May 19 2005

EXTENSIONS

More terms from Michel Marcus, May 17 2014

STATUS

approved

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Last modified October 20 13:41 EDT 2019. Contains 328257 sequences. (Running on oeis4.)