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 A280448 #19 Jun 19 2019 21:06:57
%S A280448 1,3,4,4,6,10,9,7,6,20,15,11,17,28,19,11,23,23,25,27,36,48,30,24,12,
%T A280448 55,16,35,39,56,41,20,55,73,55,44,50,81,65,39,53,96,56,71,33,97,63,40,
%U A280448 29,53,88,83,71,63,91,68,98,126,78,87,80,134,65,40,107,147,89,107,119
%N A280448 Sum of the GCDs of the smaller and larger parts of the partitions of 2n into two squarefree parts.
%H A280448 <a href="/index/Par#part">Index entries for sequences related to partitions</a>
%F A280448 a(n) = Sum_{i=1..n} gcd(i,2n-i) * mu(i)^2 * mu(2n-i)^2, where mu is the Möbius function (A008683).
%p A280448 with(numtheory): A280448:=n->add(gcd(2*n-i, i)*mobius(i)^2*mobius(2*n-i)^2, i=1..n): seq(A280448(n), n=1..100);
%t A280448 Table[Sum[GCD[k, 2*n - k]*MoebiusMu[k]^2 * MoebiusMu[2*n - k]^2, {k, 1,
%t A280448 n}], {n, 1, 50}] (* _G. C. Greubel_, Jan 05 2017 *)
%o A280448 (PARI) for(n=1,50, print1(sum(k=1,n, gcd(k,2*n-k) * (moebius(k))^2 *(moebius(2*n-k))^2), ", ")) \\ _G. C. Greubel_, Jan 05 2017
%Y A280448 Cf. A008683, A234307, A280226.
%K A280448 nonn,easy
%O A280448 1,2
%A A280448 _Wesley Ivan Hurt_, Jan 03 2017