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Numbers n such that Sum_{d|n} 1/sigma(d) > Sum_{d|m} 1/sigma(d) for all m < n.
8

%I #8 Sep 08 2022 08:46:15

%S 1,2,4,6,12,24,30,36,48,60,120,180,240,360,420,720,840,1260,1680,2520,

%T 5040,10080,13860,15120,18480,25200,27720,55440,110880,166320,277200,

%U 332640,360360,720720,1441440,2162160,3603600,4324320,6126120,7207200,10810800,12252240,21621600,24504480,36756720,61261200,73513440

%N Numbers n such that Sum_{d|n} 1/sigma(d) > Sum_{d|m} 1/sigma(d) for all m < n.

%C Where record values of Sum_{d|n} 1/sigma(d) occur.

%e For n = 4; a(4) = 6 because 6 is the smallest number such that Sum_{d|a(4)} 1/sigma(d) = Sum_{d|6} 1/sigma(d) = 5/3 > Sum_{d|a(3)} 1/sigma(d) = Sum_{d|4} 1/sigma(d) = 31/21.

%o (Magma) a:=1; S:=[a]; for n in [2..25] do k:=0; flag:= true; while flag do k+:=1; if &+[1/SumOfDivisors(d): d in Divisors(a)] lt &+[1/SumOfDivisors(d): d in Divisors(k)] then Append(~S, k); a:=k; flag:=false; end if; end while; end for; S;

%o (PARI) b(n)={sumdiv(n, d, 1/sigma(d));}

%o { my(m=0); for(n=1, 1e6, if(b(n)>m, m=b(n); print1(n, ", "))) } \\ _Andrew Howroyd_, Nov 11 2018

%Y Cf. A069934, A000203, A265708, A265709, A265710, A265711, A265712, A265713, A265714, A266227.

%K nonn

%O 1,2

%A _Jaroslav Krizek_, Dec 24 2015

%E a(35)-a(47) from _Andrew Howroyd_, Nov 11 2018