A157848 - OEIS

%I #23 Jan 12 2025 11:05:50

%S 1,3,28,45,84,182,270,620,546,1240,1330,1638,1260,1365,2660,8128,6200,

%T 6200,6944,8190,9310,7560,8190,18600,15120,18620,16380,25935,30240,

%U 32760,63700,55860,40950,55800,117800,98208,105664,117800,121030,173600,167400,155610

%N Corresponding values of arithmetic means of divisors of numbers from A007340.

%C A007340 = numbers k such that the arithmetic mean of divisors of k is an integer and equal to one of the divisors of this numbers.

%H Amiram Eldar, <a href="/A157848/b157848.txt">Table of n, a(n) for n = 1..847</a> (calculated from the b-file at A007340)

%F a(n) = sigma(A007340(n))/tau(A007340(n)) = A000203(A007340(n))/A000005(A007340(n)).

%e a(3) = 28, because 28 is arithmetic mean of divisors of A007340(3)=140 and also is divisor of 140.

%o [SumOfDivisors(n) / NumberOfDivisors(n): n in[A007340(n)] ]

%o (PARI) lista(kmax) = {my(f, s, d); for(k = 1, kmax, f = factor(k); s = sigma(f); d = numdiv(f); if(!(s % d) && denominator(d / sigma(f, -1)) == 1, print1(s/d, ", ")));} \\ _Amiram Eldar_, Apr 15 2024

%Y Cf. A000203, A007340, A000005.

%K nonn

%O 1,2

%A _Jaroslav Krizek_, Mar 07 2009, Mar 09 2009

%E Corrected and extended by _Jaroslav Krizek_, Mar 29 2015