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 A099940 #14 Feb 16 2025 08:32:55
%S A099940 2,1,1,1,5,1,84,11,184,15,193248,23,19056960,833,33740,64035,
%T A099940 520105017600,2473,130859579289600,203685,963513600,23748417,
%U A099940 16397141420298240000,645119,555804546402631680,8527366575
%N A099940 a(n) = 2*(A056855(n)) /(phi(n)*n), where phi() is the Euler phi function.
%C A099940 Conjecture: this sequence consists completely of integers.
%C A099940 From Leudesdorf's theorem this is an integer sequence. - _Benoit Cloitre_, Nov 13 2004
%D A099940 G. H. Hardy and E. M. Wright, Introduction to the theory of numbers, fifth edition, Oxford Science Publication, pp. 100-102
%H A099940 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LeudesdorfTheorem.html">Leudesdorf Theorem</a>
%H A099940 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BauersIdenticalCongruence.html">Bauers Identical Congruence</a>
%e A099940 a(6) = 2*(1 + 1/5)*1*5/(6*2) = 1.
%t A099940 f[n_] := Block[{k = Select[Range[n], GCD[ #, n] == 1 &]}, 2Plus @@ (Times @@ k*Plus @@ 1/k)/EulerPhi[n]/n]; Table[ f[n], {n, 26}] (* _Robert G. Wilson v_, Nov 16 2004 *)
%Y A099940 Cf. A056855, A000010.
%Y A099940 Cf. A093600.
%K A099940 nonn
%O A099940 1,1
%A A099940 _Leroy Quet_, Nov 12 2004
%E A099940 More terms from _Don Reble_, Nov 12 2004, who remarks that the conjecture is true for n <= 5000.