This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A245785 #11 Jun 02 2025 10:13:30 %S A245785 1,2,6,12,10,2,14,8,9,10,22,3,26,14,20,80,34,6,38,30,84,22,46,2,75,26, %T A245785 108,3,58,20,62,96,44,34,140,36,74,38,156,4,82,28,86,33,30,46,94,60, %U A245785 147,150,68,78,106,36,220,7,228,58,118,5,122,62,126,448,260 %N A245785 Denominator of (n/tau(n) + sigma(n)/n). %C A245785 Denominator of (n/A000005(n) + A000203(n)/n). %C A245785 See A245784 - numerator of (n/tau(n) + sigma(n)/n). %C A245785 A245784(n) / a(n) = integer for numbers n in A245786; a(n) = 1. %C A245785 First deviation from A245777 (denominator of (n/tau(n) - sigma(n)/n)) is at a(300); a(300) = 25, A245777(300) = 75. Sequence of numbers n such that A245777(n) is not equal to a(n): 300, 768, 1452, 1764, 2100, 3468, 3900, 5376, 5700, 6084, 6348, 9075, 9300, ... See (Magma) [n: n in [1..10000] | (Denominator((n/(#[d: d in Divisors(n)]))+(SumOfDivisors(n)/n))) - (Denominator((n/(#[d: d in Divisors(n)]))-(SumOfDivisors(n)/n))) ne 0] %H A245785 Jaroslav Krizek, <a href="/A245785/b245785.txt">Table of n, a(n) for n = 1..10000</a> %e A245785 For n = 9; a(9) = denominator(9/tau(9) + sigma(9)/9) = denominator(9/3 + 13/9) = denominator(40/9) = 9. %o A245785 (Magma) [Denominator((n/(#[d: d in Divisors(n)]))+(SumOfDivisors(n)/n)): n in [1..1000]] %o A245785 (PARI) for(n=1, 100, s=n/numdiv(n); t=sigma(n)/n; print1(denominator(s+t),", ")) \\ _Derek Orr_, Aug 15 2014 %Y A245785 Cf. A000005, A000203, A245784, A245786. %K A245785 nonn,frac %O A245785 1,2 %A A245785 _Jaroslav Krizek_, Aug 15 2014