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 A034743 #19 Sep 08 2019 12:24:20
%S A034743 1,0,1,4,14,50,202,872,4138,21132,115974,678514,4213596,27644234,
%T A034743 190899306,1382957668,10480142146,82864865614,682076806158,
%U A034743 5832742183906,51724158235168,474869816040776,4506715738447322
%N A034743 a(n) = Sum_{d | n} mu(n/d) * Bell(d-1).
%C A034743 A kind of Dirichlet convolution of mu(n) with Bell numbers.
%H A034743 Andrew Howroyd, <a href="/A034743/b034743.txt">Table of n, a(n) for n = 1..100</a>
%t A034743 a[n_] := Sum[MoebiusMu[n/d]*BellB[d - 1], {d, Divisors[n]}];
%t A034743 Array[a, 23] (* _Jean-François Alcover_, Sep 08 2019 *)
%o A034743 (PARI)
%o A034743 bell(n) = sum(k=0,n,stirling(n,k,2));
%o A034743 a(n) = sumdiv(n,d, moebius(n/d) * bell(d-1)); \\ _Andrew Howroyd_, Apr 03 2017
%Y A034743 Cf. A000110, A008683, A082951.
%K A034743 nonn
%O A034743 1,4
%A A034743 _Erich Friedman_
%E A034743 More precise definition from _Andrew Howroyd_, Apr 03 2017