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 A299788 #59 Mar 02 2025 14:33:57
%S A299788 1,2,3,8,5,1,7,64,27,25,11,3,13,49,25,1024,17,27,19,1000,441,121,23,
%T A299788 16,125,169,729,7,29,625,31,32768,121,289,1225,5832,37,361,1521,6400,
%U A299788 41,2401,43,1331,3375,529,47,3072,343,31250,289,17576,53,6561,3025,49
%N A299788 a(n) = denominator of Product_{d|n} (sigma(d)/d) where sigma(k) = the sum of the divisors of k (A000203).
%F A299788 a(n) = 1 for n = 1, 6, ... (no other n <= 5*10^6).
%F A299788 a(n) = n for n = primes (A000040).
%F A299788 a(n) = n * sqrt(n) for n in A280076 (union of 1 and squares of primes (A001248)).
%e A299788 For n=4; Product_{d|4} (sigma(d)/d) = (sigma(1)/1)*(sigma(2)/2)*(sigma(4)/4) = (1/1)*(3/2)*(7/4) = 21/8; a(4) = 8.
%t A299788 Array[Denominator@ Product[DivisorSigma[1, d]/d, {d, Divisors@ #}] &, 51]
%o A299788 (Magma) [Denominator(&*[&+[c: c in Divisors(d)] / d: d in Divisors(n)]): n in [1..100]];
%o A299788 (PARI) a(n) = my(p=1); fordiv(n, d, p *= sigma(d)/d); denominator(p); \\ _Michel Marcus_, Jan 21 2019
%Y A299788 Cf. A000203, A318491, A318492, A322673 (numerator).
%K A299788 nonn,frac
%O A299788 1,2
%A A299788 _Jaroslav Krizek_, Jan 21 2019