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 A323780 #10 Sep 08 2022 08:46:23
%S A323780 1,3,2,21,3,2,4,105,26,9,6,7,7,12,1,3255,9,26,10,63,8,18,12,35,93,21,
%T A323780 65,21,15,3,16,1085,4,27,3,91,19,6,7,315,21,8,22,9,13,36,24,2170,76,
%U A323780 279,3,147,27,39,9,21,20,9,30,21,31,48,104,137795,21,12,34
%N A323780 a(n) = denominator of Sum_{d|n} (tau(d)/sigma(d)) where tau(k) = the number of the divisors of k (A000005) and sigma(k) = the sum of the divisors of k (A000203).
%C A323780 Sum_{d|n} (tau(d)/sigma(d)) >= 1 for all n >= 1.
%F A323780 a(p) = (p+1) / gcd(p+3, p+1) for p = primes p.
%F A323780 a(n) = 1 for numbers in A323781.
%e A323780 For n=4; Sum_{d|4} (tau(d)/sigma(d)) = (tau(1)/sigma(1))+(tau(2)/sigma(2))+(tau(4)/sigma(4)) = (1/1)+(2/3)+(3/7) = 44/21; a(4) = 21.
%t A323780 Array[Denominator@ DivisorSum[#, Divide @@ DivisorSigma[{0, 1}, #] &] &, 67] (* _Michael De Vlieger_, Feb 15 2019 *)
%o A323780 (Magma) [Denominator(&+[NumberOfDivisors(d) / SumOfDivisors(d): d in Divisors(n)]): n in [1..100]]
%o A323780 (PARI) a(n) = denominator(sumdiv(n, d, numdiv(d)/sigma(d))); \\ _Michel Marcus_, Feb 13 2019
%Y A323780 Cf. A000005, A000203, A323779 (numerator), A323781.
%K A323780 nonn,frac
%O A323780 1,2
%A A323780 _Jaroslav Krizek_, Feb 13 2019