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 A306896 #11 Mar 18 2019 19:30:10
%S A306896 0,6,6,24,30,84,126,288,522,1080,2046,4224,8190,16548,32850,65856,
%T A306896 131070,262836,524286,1049760,2097438,4196412,8388606,16782048,
%U A306896 33554550,67117128,134218782,268452240,536870910,1073777040,2147483646,4295033472,8589938742,17180000352,34359739050
%N A306896 a(n) = Sum_{d|n} (2^d + 2*(-1)^d)*phi(n/d).
%H A306896 Michael De Vlieger, <a href="/A306896/b306896.txt">Table of n, a(n) for n = 1..3321</a>
%H A306896 Dennis S. Bernstein, Omran Kouba, <a href="https://arxiv.org/abs/1901.10703">Counting Colorful Necklaces and Bracelets in Three Colors</a>, arXiv:1901.10703 [math.CO], 2019.
%p A306896 See A306888.
%t A306896 Table[DivisorSum[n, (2^# + 2 (-1)^#) EulerPhi[n/#] &], {n, 35}] (* _Michael De Vlieger_, Mar 18 2019 *)
%o A306896 (PARI) a(n) = sumdiv(n, d, (2^d + 2*(-1)^d)*eulerphi(n/d)); \\ _Michel Marcus_, Mar 16 2019
%Y A306896 Cf. A306888, A306897.
%K A306896 nonn
%O A306896 1,2
%A A306896 _Michael De Vlieger_ and _N. J. A. Sloane_, Mar 15 2019