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A240923 a(n) = numerator(sigma(n)/n) - sigma(denominator(sigma(n)/n)). 4
0, 0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 3, 0, 4, 2, 0, 0, 1, 0, 3, 0, 6, 0, 2, 0, 7, 0, 1, 0, 6, 0, 0, 4, 9, 0, 0, 0, 10, 0, 2, 0, 8, 0, 9, 2, 12, 0, 3, 0, 0, 6, 7, 0, 7, 0, 7, 0, 15, 0, 8, 0, 16, 0, 0, 0, 12, 0, 9, 8, 24, 0, 5, 0, 19, 0, 15, 0, 14, 0, 3, 0, 21, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,10
COMMENTS
a(n) is the integer t, such that if sigma(n)/n is written in its reduced form, nk/dk = A017665(n)/A017666(n), then we have (sigma(dk)+t)/dk.
It appears that a(n) is never negative.
a(n) = 0 if and only if n is in A014567 (n and sigma(n) are relatively prime).
LINKS
William G. Stanton and Judy A. Holdener, Abundancy "Outlaws" of the Form (sigma(N) + t)/N, Journal of Integer Sequences , Vol 10 (2007) , Article 07.9.6.
EXAMPLE
For n=10, sigma(10)/10 = 18/10 = 9/5 = (sigma(5) + 3)/5, hence a(10)=3.
MAPLE
with(numtheory): A240923:=n->numer(sigma(n)/n) - sigma(denom(sigma(n)/n)): seq(A240923(n), n=1..100); # Wesley Ivan Hurt, Aug 06 2014
MATHEMATICA
Table[Numerator[DivisorSigma[1, n]/n] - DivisorSigma[1, Denominator[ DivisorSigma[1, n]/n]], {n, 100}] (* Wesley Ivan Hurt, Aug 06 2014 *)
PROG
(PARI) a(n) = my(ab = sigma(n)/n); numerator(ab) - sigma(denominator(ab));
(Haskell)
import Data.Ratio ((%), numerator, denominator)
a240923 n = numerator sq - a000203 (denominator sq)
where sq = a000203 n % n
-- Reinhard Zumkeller, Aug 05 2014
(Python)
from gmpy2 import mpq
from sympy import divisors
map(lambda x: x.numerator-sum(divisors(x.denominator)), [mpq(sum(divisors(n)), n) for n in range(1, 10**5)]) # Chai Wah Wu, Aug 05 2014
CROSSREFS
Cf. A000203.
Sequence in context: A297871 A292130 A291971 * A272727 A333791 A323135
KEYWORD
nonn
AUTHOR
Michel Marcus, Aug 03 2014
STATUS
approved

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Last modified March 28 13:42 EDT 2024. Contains 371254 sequences. (Running on oeis4.)