A379516 Denominators of the partial alternating sums of the reciprocals of the sum of unitary divisors function (A034448).

1, 3, 12, 60, 60, 5, 40, 360, 360, 120, 120, 120, 840, 140, 840, 14280, 42840, 42840, 42840, 8568, 34272, 34272, 34272, 11424, 148512, 49504, 7072, 35360, 106080, 318240, 159120, 1750320, 109395, 656370, 5250960, 26254800, 498841200, 498841200, 3491888400, 3491888400

Offset: 1

Author

Amiram Eldar, Dec 23 2024

Keywords

• nonn
• easy
• frac

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000
• Olivier Bordellès and Benoit Cloitre, An Alternating Sum Involving the Reciprocal of Certain Multiplicative Functions, Journal of Integer Sequences, Vol. 16 (2013), Article 13.6.3. See p. 4, eq. (vi).
• László Tóth, Alternating Sums Concerning Multiplicative Arithmetic Functions, Journal of Integer Sequences, Vol. 20 (2017), Article 17.2.1. See section 4.9, pp. 28-29.

Crossrefs

Cf. A034448, A064609, A370898, A379514, A379515 (numerators).

Programs

Mathematica

usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); usigma[1] = 1; Denominator[Accumulate[Table[(-1)^(n+1)/usigma[n], {n, 1, 50}]]]

PARI

usigma(n) = {my(f = factor(n)); prod(i = 1, #f~, 1 + f[i, 1]^f[i, 2]);}
list(nmax) = {my(s = 0); for(k = 1, nmax, s += (-1)^(k+1) / usigma(k); print1(denominator(s), ", "))};

Formula

a(n) = denominator(Sum_{k=1..n} (-1)^(k+1)/A034448(k)).