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 A130089 #12 Feb 12 2019 01:16:04
%S A130089 1,1,2,3,12,20,45,14,70,864,525,880,6237,3328,3003,900,25025,60928,
%T A130089 53703,19456,3997125,1209600,3556553,30912,67643667,11264000,244375,
%U A130089 26687232,52055003,2702336,351469125,90272000,47453715,1284636672
%N A130089 a(n) = denominator of Product_{k=1..n} k^mu(n+1-k), where mu(k) = A008683(k).
%e A130089 a(5) = denominator(1^(-1)*2^(0)*3^(-1)*4^(-1)*5^(1)) = denominator(5/12) = 12.
%p A130089 with(numtheory): a:=n->denom(mul(k^mobius(n+1-k),k=1..n)): seq(a(n),n=1..41); # _Emeric Deutsch_, May 09 2007
%o A130089 (PARI) a(n) = denominator(prod(k=1, n, k^moebius(n+1-k))); \\ _Michel Marcus_, Feb 12 2019
%Y A130089 Cf. A130086, A130087, A130088.
%K A130089 frac,nonn
%O A130089 1,3
%A A130089 _Leroy Quet_, May 06 2007
%E A130089 More terms from _Emeric Deutsch_, May 09 2007