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A168129 Numbers sigma(k) when Sum_(j=1..k) sigma(j) / sigma(k) is an integer. 3
1, 4, 30, 444, 1767, 86250, 97920, 185700, 584640, 21954842, 17654544432, 357550809280, 709346653572, 1061551370880 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Numbers A000203(k) when A024916(k) / A000203(k) is an integer.
Corresponding values of k, Sum_(j=1..k) sigma(k) and Sum_(j=1..k) sigma(j)/sigma(k) are given in A168127, A168130 and A168128. - Jaroslav Krizek, Nov 21 2009
LINKS
FORMULA
a(n) = A000203(A168127(n)). - Michel Marcus, Feb 22 2020
EXAMPLE
a(3) = 30 because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer, where 29 is A168127(3).
PROG
(PARI) v=vector(10); c=0; m=0; for(k=1, 11413204, s=sigma(k); m=m+s; if(m%s==0, c++; v[c]=s)); v=vecsort(v); for(i=1, c, print1(v[i] ", ")) \\ Donovan Johnson, Oct 16 2013
CROSSREFS
Sequence in context: A326205 A351795 A290058 * A193500 A163885 A120338
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Nov 18 2009, Dec 04 2009
EXTENSIONS
a(8)-a(10) from Donovan Johnson, Oct 16 2013
a(11)-a(14) from Giovanni Resta, Jun 06 2016
Name edited by Michel Marcus, Feb 22 2020
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)