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A088838 Numerator of the quotient sigma(3n)/sigma(n). 4
4, 4, 13, 4, 4, 13, 4, 4, 40, 4, 4, 13, 4, 4, 13, 4, 4, 40, 4, 4, 13, 4, 4, 13, 4, 4, 121, 4, 4, 13, 4, 4, 13, 4, 4, 40, 4, 4, 13, 4, 4, 13, 4, 4, 40, 4, 4, 13, 4, 4, 13, 4, 4, 121, 4, 4, 13, 4, 4, 13, 4, 4, 40, 4, 4, 13, 4, 4, 13, 4, 4, 40, 4, 4, 13, 4, 4, 13, 4, 4, 364, 4, 4, 13, 4, 4, 13, 4, 4, 40 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

From Robert Israel, Nov 19 2017: (Start)

a(n) = (3^(2+A007949(n))-1)/2.

G.f.: Sum_{k>=0} (3^(k+2)-1)*(x^(3^k)+x^(2*3^k))/(2*(1-x^(3^(k+1)))).

(End)

MAPLE

A088838 := proc(n)

    numtheory[sigma](3*n)/numtheory[sigma](n) ;

    numer(%) ;

end proc:

seq(A088838(n), n=1..100) ; # R. J. Mathar, Nov 19 2017

seq((3^(2+padic:-ordp(n, 3))-1)/2, n=1..100); # Robert Israel, Nov 19 2017

MATHEMATICA

k=3; Table[Numerator[DivisorSigma[1, k*n]/DivisorSigma[1, n]], {n, 1, 128}]

PROG

(PARI) a(n) = numerator(sigma(3*n)/sigma(n)) \\ Felix Fröhlich, Nov 19 2017

CROSSREFS

Cf. A007949, A038712, A088837, A088839, A088840, A080278 (denominator), A000203.

Sequence in context: A228612 A038804 A183362 * A127403 A276423 A052993

Adjacent sequences:  A088835 A088836 A088837 * A088839 A088840 A088841

KEYWORD

easy,nonn,frac,look

AUTHOR

Labos Elemer, Nov 04 2003

STATUS

approved

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Last modified July 22 10:41 EDT 2019. Contains 325219 sequences. (Running on oeis4.)