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A265392 a(n) = denominator of Sum_{d|n} 1 / tau(d). 7
1, 2, 2, 6, 2, 4, 2, 12, 6, 4, 2, 4, 2, 4, 4, 60, 2, 4, 2, 4, 4, 4, 2, 8, 6, 4, 12, 4, 2, 8, 2, 20, 4, 4, 4, 36, 2, 4, 4, 8, 2, 8, 2, 4, 4, 4, 2, 40, 6, 4, 4, 4, 2, 8, 4, 8, 4, 4, 2, 8, 2, 4, 4, 140, 4, 8, 2, 4, 4, 8, 2, 72, 2, 4, 4, 4, 4, 8, 2, 40, 60, 4, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = denominator of Sum_{d|n} 1 / A000005(d).

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

FORMULA

a(n) = A265391(n) / [Sum_{d|n} 1 / tau(d)] = A265391(n) * A253139(n) / A265390(n).

a(1) = 1; a(p) = 2 for p = prime; a(n) = n for numbers 1, 2, 36, 72, ...

EXAMPLE

For n = 6; divisors d of 6: {1, 2, 3, 6}; tau(d): {1, 2, 2, 4}; Sum_{d|6} 1 / tau(d) = 1/1 + 1/2 + 1/2 + 1/4 = 9 / 4; a(n) = 4 (denominator).

MATHEMATICA

Table[Denominator[Sum[1/DivisorSigma[0, d], {d, Divisors@ n}]], {n, 83}] (* Michael De Vlieger, Dec 09 2015 *)

PROG

(MAGMA) [Denominator(&+[1/NumberOfDivisors(d): d in Divisors(n)]): n in [1..1000]]

(PARI) a(n) = denominator(sumdiv(n, d, 1/numdiv(d))); \\ Michel Marcus, Dec 09 2015

CROSSREFS

Cf. A000005, A253139, A265390, A265391 (numerator), A265392, A265393.

Sequence in context: A129750 A278234 A068976 * A253139 A318519 A317848

Adjacent sequences:  A265389 A265390 A265391 * A265393 A265394 A265395

KEYWORD

nonn,frac

AUTHOR

Jaroslav Krizek, Dec 08 2015

STATUS

approved

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Last modified April 18 08:37 EDT 2019. Contains 322209 sequences. (Running on oeis4.)