Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #9 Sep 08 2022 08:46:08
%S 1,3,4,7,6,1,8,15,13,9,12,7,14,6,8,31,18,13,20,21,32,9,24,5,31,21,40,
%T 1,30,1,32,63,16,27,48,91,38,15,56,9,42,2,44,21,26,18,48,31,57,93,8,
%U 49,54,5,72,15,80,45,60,7,62,24,104,127,84,1,68,63,32,9
%N Denominators of (product of divisors of n / sum of divisors of n).
%C Denominators of (A007955(n) / A000203(n)).
%C For numerators see A244668.
%F a(n) = 1 for numbers from A145551 (numbers n such that product of divisors of n / sum of divisors of n is an integer).
%e a(8) = 15 because A007955(8) / A000203(8) = 64 / 15.
%o (Magma)[Denominator((&*[d: d in Divisors(n)]) / (&+[d: d in Divisors(n)])): n in [1..1000]]
%o (PARI) a007955(n)=if(issquare(n, &n), n^numdiv(n^2), n^(numdiv(n)/2)) ;
%o a(n) = denominator(a007955(n)/sigma(n)); \\ _Michel Marcus_, Jul 05 2014
%Y Cf. A007955, A000203, A145551, A244668, A244670.
%K nonn,frac
%O 1,2
%A _Jaroslav Krizek_, Jul 04 2014