A168127
Numbers k such that Sum_{j=1..k} sigma(j) / sigma(k) is an integer.
Original entry on oeis.org
1, 3, 29, 365, 1225, 81595, 86249, 185699, 582917, 11413204, 16646745763, 311408527843, 709342670921, 881267828693
Offset: 1
29 is in the sequence because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer.
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m=0; for(k=1, 11413204, s=sigma(k); m=m+s; if(m%s==0, print1(k ", "))) \\ Donovan Johnson, Oct 16 2013
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isok(k) = (sum(j=1, k, sigma(j)) % sigma(k)) == 0; \\ Michel Marcus, Feb 19 2020
A168128
Numbers Sum_(j=1..k) sigma(j) / sigma(k) when this expression is an integer.
Original entry on oeis.org
1, 2, 23, 247, 699, 55921, 70936, 152730, 478017, 4879815, 12909834588, 223070292558, 583407686653, 601718433498
Offset: 1
a(3)=23 because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer, where 29 is A168127(3).
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m=0; for(k=1, 11413204, s=sigma(k); m=m+s; if(m%s==0, print1(m/s ", "))) \\ Donovan Johnson, Oct 16 2013
A168129
Numbers sigma(k) when Sum_(j=1..k) sigma(j) / sigma(k) is an integer.
Original entry on oeis.org
1, 4, 30, 444, 1767, 86250, 97920, 185700, 584640, 21954842, 17654544432, 357550809280, 709346653572, 1061551370880
Offset: 1
a(3) = 30 because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer, where 29 is A168127(3).
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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
Showing 1-3 of 3 results.
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