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 A345131 #41 Jun 19 2021 04:58:05
%S A345131 1,2,8,29,118,427,1671,6260,24034,91301,351261,1345434,5191170,
%T A345131 20018845,77500485,300290041,1166450850,4535971707,17670369300,
%U A345131 68913194733,269114332057,1051984590581,4116622325140,16123381985750,63204699026898,247956554702702
%N A345131 Number of ordered n-tuples of integers from [ 1..n ] with no global factor.
%H A345131 Seiichi Manyama, <a href="/A345131/b345131.txt">Table of n, a(n) for n = 1..1000</a>
%F A345131 a(n) = Sum_{k=1..n} Sum_{d|k} mu(k/d) * binomial(d+n-2, d-1).
%F A345131 a(n) = [x^n] (1/(1 - x)) * Sum_{k>=1} mu(k) * x^k / (1 - x^k)^n.
%F A345131 a(n) ~ 2^(2*n-1) / sqrt(Pi*n). - _Vaclav Kotesovec_, Jun 19 2021
%t A345131 a[n_] := Sum[DivisorSum[k, MoebiusMu[k/#] * Binomial[n + # - 2, # - 1] &], {k, 1, n}]; Array[a, 25] (* _Amiram Eldar_, Jun 13 2021 *)
%o A345131 (PARI) a(n) = sum(k=1, n, sumdiv(k, d, moebius(k/d)*binomial(d+n-2, d-1)));
%Y A345131 Main diagonal of A177976.
%Y A345131 Cf. A332470.
%K A345131 nonn
%O A345131 1,2
%A A345131 _Seiichi Manyama_, Jun 12 2021