OFFSET
1,2
COMMENTS
Sum of the divisors d1 from the ordered pairs of divisors of n, (d1,d2) with d1<=d2, such that d1|d2. - Wesley Ivan Hurt, Mar 22 2022
a(n) is the sum of the sum-of-divisors of the divisors of n. - M. F. Hasler, Mar 29 2024
REFERENCES
David M. Burton, Elementary Number Theory, Allyn and Bacon Inc., Boston, MA, 1976, p. 120.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Travis Scholl, Table of n, a(n) for n = 1..100000 (terms 1 through 1000 were by T. D. Noe)
Olivier Bordelles, Mean values of generalized gcd-sum and lcm-sum functions, JIS, Vol. 10 (2007), Article 07.9.2, series g_4 (with an apparently wrong D.g.f. after equation 3).
N. J. A. Sloane, Transforms.
FORMULA
a(n) = Sum_{d|n} d*tau(n/d). - Vladeta Jovovic, Jul 31 2002
Multiplicative with a(p^e) = (p*(p^(e+1)-1)-(p-1)*(e+1))/(p-1)^2. - Vladeta Jovovic, Dec 25 2001
G.f.: Sum_{k>=1} sigma(k)*x^k/(1-x^k). - Benoit Cloitre, Apr 21 2003
Moebius transform of A007430. - Benoit Cloitre, Mar 03 2004
Dirichlet g.f.: zeta(s-1)*zeta^2(s).
Equals A051731^2 * [1, 2, 3, ...]. Equals row sums of triangle A134577. - Gary W. Adamson, Nov 02 2007
Row sums of triangle A134699. - Gary W. Adamson, Nov 06 2007
L.g.f.: -log(Product_{k>=1} (1 - x^k)^(sigma(k)/k)) = Sum_{n>=1} a(n)*x^n/n. - Ilya Gutkovskiy, May 26 2018
Sum_{k=1..n} a(k) ~ c * n^2, where c = Pi^4/72 = 1.352904... (A152649). - Amiram Eldar, Oct 22 2022
MAPLE
A007429 := proc(n)
add(numtheory[sigma](d), d=numtheory[divisors](n)) ;
end proc:
seq(A007429(n), n=1..100) ; # R. J. Mathar, Aug 28 2015
MATHEMATICA
f[n_] := Plus @@ DivisorSigma[1, Divisors@n]; Array[f, 52] (* Robert G. Wilson v, May 05 2010 *)
f[p_, e_] := (p*(p^(e + 1) - 1) - (p - 1)*(e + 1))/(p - 1)^2; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Apr 10 2022 *)
PROG
(PARI) A007429_upto(N)=vector(N, n, sumdiv(n, d, sigma(d))) \\ edited by M. F. Hasler, Mar 29 2024
(PARI) a(n)=if(n<1, 0, direuler(p=2, n, 1/(1-X)^2/(1-p*X))[n]) \\ Ralf Stephan
(PARI)
N=17; default(seriesprecision, N); x=z+O(z^(N+1))
c=sum(j=1, N, j*x^j);
t=1/prod(j=1, N, eta(x^(j))^(1/j))
t=log(t)
t=serconvol(t, c)
Vec(t)
/* Joerg Arndt, May 03 2008 */
(PARI) a(n)=sumdiv(n, d, sumdiv(d, t, t ) ); /* Joerg Arndt, Oct 07 2012 */
(Sage) def A(n): return sum(sigma(d) for d in n.divisors()) # Travis Scholl, Apr 14 2016
(Magma) [&+[SumOfDivisors(d): d in Divisors(n)]: n in [1..100]] // Jaroslav Krizek, Sep 24 2016
(Python)
from math import prod
from sympy import factorint
def A007429(n): return prod((p*(p**(e+1)-1)-(p-1)*(e+1))//(p-1)**2 for p, e in factorint(n).items()) # Chai Wah Wu, Mar 28 2024
CROSSREFS
KEYWORD
nonn,easy,nice,mult
AUTHOR
STATUS
approved