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A320940 a(n) = Sum_{d|n} d*sigma_n(d). 4
1, 11, 85, 1127, 15631, 287021, 5764809, 135007759, 3487020610, 100146496681, 3138428376733, 107032667155169, 3937376385699303, 155582338242604221, 6568408966322733475, 295154660699054931999, 14063084452067724991027, 708239400347943609329270 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..385

N. J. A. Sloane, Transforms

FORMULA

a(n) = n * [x^n] -log(Product_{k>=1} (1 - x^k)^sigma_n(k)).

a(n) = Sum_{d|n} d^(n+1)*sigma_1(n/d).

a(n) ~ n^(n+1). - Vaclav Kotesovec, Feb 16 2020

EXAMPLE

a(6) = 1*sigma_6(1)+2*sigma_6(2)+3*sigma_6(3)+6*sigma_6(6) = 1+2*65+3*730+6*47450 = 287021.

MAPLE

with(numtheory): seq(coeff(series(n*(-log(mul((1-x^k)^sigma[n](k), k=1..n))), x, n+1), x, n), n = 1 .. 20); # Muniru A Asiru, Oct 28 2018

MATHEMATICA

Table[Sum[d DivisorSigma[n, d], {d, Divisors[n]}] , {n, 18}]

Table[n SeriesCoefficient[-Log[Product[(1 - x^k)^DivisorSigma[n, k], {k, 1, n}]], {x, 0, n}], {n, 18}]

PROG

(PARI) a(n) = sumdiv(n, d, d*sigma(d, n)); \\ Michel Marcus, Oct 28 2018

(Python)

from sympy import divisor_sigma, divisors

def A320940(n):

    return sum(divisor_sigma(d)*(n//d)**(n+1) for d in divisors(n, generator=True)) # Chai Wah Wu, Feb 15 2020

(MAGMA) [&+[d*DivisorSigma(n, d):d in Divisors(n)]:n in [1..18]]; // Marius A. Burtea, Feb 15 2020

CROSSREFS

Cf. A000203, A001001, A027847, A027848, A319647, A321141.

Sequence in context: A001240 A129180 A082365 * A012794 A302954 A014917

Adjacent sequences:  A320937 A320938 A320939 * A320941 A320942 A320943

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Oct 28 2018

STATUS

approved

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Last modified April 14 16:19 EDT 2021. Contains 342949 sequences. (Running on oeis4.)