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A072692 Sum of sigma(j) for 1<=j<=10^n, where sigma(j) is the sum of the divisors of j. 9
1, 87, 8299, 823081, 82256014, 8224740835, 822468118437, 82246711794796, 8224670422194237, 822467034112360628, 82246703352400266400, 8224670334323560419029, 822467033425357340138978, 82246703342420509396897774, 8224670334241228180927002517 (list; graph; refs; listen; history; text; internal format)
P. L. Patodia, Seth Troisi and Hiroaki Yamanouchi, Table of n, a(n) for n = 0..36 (terms a(0)-a(18) by P. L. Patodia and a(19)-a(24) by Seth Troisi)
Leonhard Euler, Découverte d'une loi tout extraordinaire des nombres par rapport à la somme de leurs diviseurs, 1747, The Euler Archive, (Eneström Index) E175.
P. L. Patodia (pannalal(AT), PARI program for A072692 and A024916
Asymptotic formula: a(n) ~ Pi^2/12 * 10^2n. See A072691 for Pi^2/12. Observe that A025281 also contains that constant in its asymptotic formula.
For n=1, the sum of sigma(j) for j<=10 is 1+3+4+7+6+12+8+15+13+18=87, so a(1)=87 (=69+18=A049000(1)+A046915(1)).
(PARI) for(m=0, 10, print1(sum(n=1, k=10^m, n*(k\n)), ", ")) \\ Improved by M. F. Hasler, Apr 18 2015
(Python) [(i, sum([d*(10**i//d) for d in range(1, 10**i+1)])) for i in range(8)] # Seth A. Troisi, Jun 27 2010
from math import isqrt
def A072692(n): return -(s:=isqrt(m:=10**n))**2*(s+1)+sum((q:=m//k)*((k<<1)+q+1) for k in range(1, s+1))>>1 # Chai Wah Wu, Oct 23 2023
(PARI) A072692(n)=A024916(10^n) \\ This is very efficient, using efficient code of A024916. - M. F. Hasler, Apr 18 2015
Compare with A049000. Note that a(n) = A049000(n) + A046915(n).
Cf. A000203 (sigma(n)), A072691 (Pi^2/12), A049000, A046915, A024916, A025281.
Sequence in context: A017750 A291130 A183040 * A287590 A133391 A298832
Rick L. Shepherd, Jul 02 2002
More terms from P L Patodia (pannalal(AT), Jan 11 2008, Jun 25 2008
Corrected by N. J. A. Sloane, Jun 08 2008, following suggestions from Don Reble and David W. Wilson

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