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 A048049 #20 Feb 16 2025 08:32:39
%S A048049 1,1,2,1,4,4,12,6,3,12,60,15,60,60,120,30,240,80,720,720,720,720,7920,
%T A048049 7920,1584,1584,1584,1584,11088,11088,55440,13860,1386,11088,11088,
%U A048049 11088,11088,11088,11088,5544,6930,13860,13860,3465,27720,27720,637560,1275120,182160
%N A048049 Denominator of Sum_{k=1..n} 1/phi(k).
%D A048049 József Sándor, Dragoslav S. Mitrinovic, and Borislav Crstici, Handbook of Number Theory I, Springer Science & Business Media, 2005, Section I.27, page 29.
%H A048049 Robert Israel, <a href="/A048049/b048049.txt">Table of n, a(n) for n = 1..10000</a>
%H A048049 R. Sitaramachandrarao, <a href="https://www.jstor.org/stable/44236939">On an error term of Landau - II</a>, The Rocky Mountain Journal of Mathematics, Vol. 15, No. 2 (1985), pp. 579-588.
%H A048049 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TotientSummatoryFunction.html">Totient Summatory Function</a>.
%e A048049 1, 2, 5/2, 3, 13/4, 15/4, 47/12, 25/6, 13/3, 55/12, 281/60, 74/15, ...
%p A048049 map(denom, ListTools:-PartialSums(map(1/numtheory:-phi, [$1..100]))); # _Robert Israel_, Apr 16 2019
%t A048049 Denominator[Accumulate[Table[1/EulerPhi[k], {k, 1, 50}]]] (* _Amiram Eldar_, Sep 18 2022 *)
%o A048049 (PARI) a(n) = denominator(sum(k=1, n, 1/eulerphi(k))); \\ _Michel Marcus_, Sep 18 2022
%Y A048049 Cf. A000010, A028415 (numerators).
%K A048049 nonn,frac
%O A048049 1,3
%A A048049 _N. J. A. Sloane_, Jun 28 2002