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 A006876 M2883 #26 Nov 04 2024 04:26:03
%S A006876 1,0,1,3,11,20,57,108,240,472,1013,1959,4083,8052,16315,32496,65519,
%T A006876 130464,262125,523209,1048353,2095084,4194281,8384100,16777120,
%U A006876 33546216,67108068,134201223,268435427,536836484,1073741793,2147417952,4294964173,8589803488,17179868739
%N A006876 Mu-molecules in Mandelbrot set whose seeds have period n.
%D A006876 B. B. Mandelbrot, The Fractal Geometry of Nature, Freeman, NY, 1982, p. 183.
%D A006876 R. Penrose, The Emperor's New Mind, Penguin Books, NY, 1991, p. 138.
%D A006876 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006876 Cheng Zhang, <a href="/A006876/b006876.txt">Table of n, a(n) for n = 1..1000</a>
%H A006876 R. P. Munafo, <a href="http://www.mrob.com/pub/muency/enumerationoffeatures.html">Enumeration of Features</a>
%F A006876 a(n) = 2*l(n) - sum_{d|n} phi(n/d)*l(d), where l(n) = sum_{d|n} mu(n/d) 2^(d-1) (A000740), and phi(n) and mu(n) are the Euler totient function (A000010) and Moebius function (A008683), respectively. - _Cheng Zhang_, Apr 02 2012
%t A006876 degRp[n_] := Sum[MoebiusMu[n/d] 2^(d - 1), {d, Divisors[n]}]; Table[degRp[n]*2 - Sum[EulerPhi[n/d] degRp[d], {d, Divisors[n]}], {n, 1, 100}] (* _Cheng Zhang_, Apr 02 2012 *)
%o A006876 (PARI) A000740(n)=sumdiv(n,d,moebius(n/d)<<(d-1))
%o A006876 a(n)=2*A000740(n)-sumdiv(n, d, eulerphi(n/d)*A000740(d)) \\ _Charles R Greathouse IV_, Feb 18 2013
%Y A006876 Cf. A006874, A006875, A000740, A118454.
%K A006876 nonn
%O A006876 1,4
%A A006876 _Robert Munafo_
%E A006876 Web link changed to more relevant page by _Robert Munafo_, Nov 16 2010
%E A006876 More terms from _Cheng Zhang_, Apr 02 2012