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A158274 Numerators of antiharmonic means of divisors of n. 2
1, 5, 5, 3, 13, 25, 25, 17, 7, 65, 61, 15, 85, 125, 65, 11, 145, 35, 181, 13, 125, 305, 265, 85, 21, 425, 41, 75, 421, 325, 481, 65, 305, 725, 325, 21, 685, 181, 425, 221, 841, 625, 925, 61, 91, 1325, 1105, 55, 43, 35 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Antiharmonic mean of divisors of number n = Product (p_i^e_i) is sigma_2(n)/sigma_1(n)= A001157(n)/A000203(n) = Product ((p_i^(e_i+1)+1)/(p_i+1)). Denominators of antiharmonic means of divisors of n: 1,3,2,1,3,6,4,3,... In A020487 numbers k = a(n) such that sigma_2(k)/sigma_1(k)= A001157(k)/A000203(k) is integers.

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

EXAMPLE

Antiharmonic means of divisors of n>=1: 1, 5/3, 5/2, 3, 13/2, 25/6, ...

MATHEMATICA

Table[Numerator[DivisorSigma[2, n]/DivisorSigma[1, n]], {n, 50}] (* Ivan Neretin, May 22 2015 *)

CROSSREFS

Cf. A001157, A000203, A020487.

Sequence in context: A232609 A225666 A175505 * A202695 A110986 A193721

Adjacent sequences:  A158271 A158272 A158273 * A158275 A158276 A158277

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Mar 15 2009

STATUS

approved

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Last modified December 16 00:33 EST 2019. Contains 330013 sequences. (Running on oeis4.)