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 A306906 #15 Dec 01 2019 23:19:06
%S A306906 1,2,6,8,15,30,49,96,189,360,693,1416,2743,5516,10980,21952,43707,
%T A306906 87642,174781,349920,699216,1398804,2796225,5594112,11184875,22372376,
%U A306906 44739810,89484080,178956999,357926040,715827913,1431677824,2863313640
%N A306906 a(n) = A306899(n)/6.
%H A306906 Michael De Vlieger, <a href="/A306906/b306906.txt">Table of n, a(n) for n = 1..3323</a>
%t A306906 Table[DivisorSum[n, (2^# - (-1)^#) EulerPhi[3 n/#] &]/6, {n, 33}] (* _Michael De Vlieger_, Dec 01 2019 *)
%o A306906 (PARI) a(n) = sumdiv(n, d, (2^d - (-1)^d)*eulerphi(3*n/d))/6; \\ _Michel Marcus_, Mar 16 2019
%Y A306906 Cf. A306899.
%K A306906 nonn
%O A306906 1,2
%A A306906 _Michael De Vlieger_ and _N. J. A. Sloane_, Mar 15 2019