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 A344431 #15 May 20 2021 07:56:05
%S A344431 1,-1,-11,-19,-654,6439,-103298,-233543,-479042,999089891,
%T A344431 -23581102192,-56760341915,-23425343599215,736752260240319,
%U A344431 31008836538146011,76278687880642289,-48483493990740616866,-121045054967668089989,-104414952870932959886007
%N A344431 a(n) = Sum_{k=1..n} mu(k) * n^(k - 1).
%H A344431 Seiichi Manyama, <a href="/A344431/b344431.txt">Table of n, a(n) for n = 1..388</a>
%t A344431 a[n_] := Sum[MoebiusMu[k] * n^(k-1), {k,1,n}]; Array[a, 20] (* _Amiram Eldar_, May 19 2021 *)
%o A344431 (PARI) a(n) = sum(k=1, n, moebius(k)*n^(k-1));
%Y A344431 Cf. A008683, A023037, A127513, A292779, A343425.
%K A344431 sign
%O A344431 1,3
%A A344431 _Seiichi Manyama_, May 19 2021