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A168130 Numbers Sum_(j=1..k) sigma(j) when Sum_(j=1..k) sigma(j) / sigma(k) is an integer. 3

%I #18 Feb 22 2020 08:31:16

%S 1,8,690,109668,1235133,5475784320,6118230000,28361961000,

%T 279467858880,107135567314230,227917248343616414016,

%U 79758963630439261338240,413838290195487519174516,638755027963568013738240

%N Numbers Sum_(j=1..k) sigma(j) when Sum_(j=1..k) sigma(j) / sigma(k) is an integer.

%C Numbers A024916(k) when A024916(k) / A000203(k) is an integer.

%C Corresponding values of k, sigma(k), and Sum_(j=1..k) sigma(j)/sigma(k) are given in A168127, A168129, and A168128. - _Jaroslav Krizek_, Nov 21 2009

%F a(n) = A024916(A168127(n)). - _Michel Marcus_, Feb 22 2020

%e a(3)= 690 = A024916(29) because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer, where 29 is A168127(3).

%o (PARI) m=0; for(k=1, 11413204, s=sigma(k); m=m+s; if(m%s==0, print1(m ", "))) \\ _Donovan Johnson_, Oct 16 2013

%Y Cf. A000203, A024916, A168127, A168128, A168129.

%K nonn,more

%O 1,2

%A _Jaroslav Krizek_, Nov 18 2009, Dec 04 2009

%E a(8)-a(10) from _Donovan Johnson_, Oct 16 2013

%E a(11)-a(14) from _Giovanni Resta_, Jun 06 2016

%E Name edited by _Michel Marcus_, Feb 22 2020

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Last modified March 19 07:21 EDT 2024. Contains 370955 sequences. (Running on oeis4.)