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 A268619 #12 Aug 24 2023 02:30:49
%S A268619 2,1,2,4,10,25,70,200,600,1845,5830,18772,61542,204659,689410,2347920,
%T A268619 8074762,28009524,97909318,344615860,1220539390,4347310451,
%U A268619 15564141262,55985418344,202256970300,733607281875,2670698800548,9755982857964,35751803209918,131405090455065,484316704740126,1789672012052256
%N A268619 a(n) = (1/n^2) * Sum_{d|n} moebius(n/d)*binomial(2*d,d).
%C A268619 6*a(n) is divisible by n (cf. A268592).
%F A268619 a(n) = (1/n^2)* Sum_{d|n} A008683(n/d)*A000984(d).
%F A268619 a(n) = A007727(n)/n^2 = A045630(n)*2/n^2 = A060165(n)/n = A022553(n)*2/n.
%t A268619 a[n_] := DivisorSum[n, MoebiusMu[n/#] * Binomial[2*#, #] &] / n^2; Array[a, 35] (* _Amiram Eldar_, Aug 24 2023 *)
%o A268619 (PARI) { a(n) = sumdiv(n, d, moebius(n/d)*binomial(2*d, d))/n^2; }
%Y A268619 Cf. A000984, A007727, A008683, A022553, A045630, A060165, A268592, A268617.
%K A268619 nonn
%O A268619 1,1
%A A268619 _Max Alekseyev_, Feb 09 2016