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 A045633 #12 Aug 28 2019 08:15:34
%S A045633 1,1,1,2,5,12,31,84,250,762,2504,8358,28928,101339,361184,1297864,
%T A045633 4707712,17179434,63068079,232615770,861723271,3204236692,11955827898,
%U A045633 44748176652,167959114814,632058070297,2384234976235,9013628450510
%N A045633 Number of 2n-bead black-white reversible complementable necklaces with n black beads and fundamental period 2n.
%H A045633 <a href="/index/Br#bracelets">Index entries for sequences related to bracelets</a>
%F A045633 Moebius transform of A006840 (Christian Bower).
%t A045633 b[n_] := (1/(2n)) DivisorSum[n, EulerPhi[n/#] Binomial[2# - 1, # - 1] + EulerPhi[2(n/#)] 2^(# - 1) &];
%t A045633 A006840[n_] := If[n == 0, 1, (b[n] + 2^(n - 2) + Binomial[n - Mod[n, 2], Quotient[n, 2]]/2)/2];
%t A045633 a[n_] := If[n == 0, 1, Sum[MoebiusMu[n/d] A006840[d], {d, Divisors[n]}]];
%t A045633 Array[a, 30, 0] (* _Jean-François Alcover_, Aug 28 2019 *)
%K A045633 nonn
%O A045633 0,4
%A A045633 _David W. Wilson_