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 A179213 #10 Mar 07 2021 03:17:54
%S A179213 3,5,14,18,28,34,55,63,80,99,132,144,170,157,202,218,285,303,378,398,
%T A179213 481,503,527,551,551,602,629,684,799,829,922,891,1022,1056,1161,1197,
%U A179213 1344,1307,1424,1464,1546,1588,1717,1761,1850,1941,2082,2130,2227,2227
%N A179213 Sum of squarefree numbers between n and 2*n (inclusive).
%H A179213 Harvey P. Dale, <a href="/A179213/b179213.txt">Table of n, a(n) for n = 1..1000</a>
%F A179213 a(n) = Sum_{k=n..2*n} k*A008966(k).
%F A179213 A073837(n) <= a(n) <= A045943(n);
%F A179213 a(n) = A066779(2*n) - A066779(n-1).
%F A179213 a(n) ~ (9/Pi^2) * n^2 + O(n^(3/2)). - _Amiram Eldar_, Mar 07 2021
%t A179213 Table[Total[Select[Range[n,2n],SquareFreeQ]],{n,50}] (* _Harvey P. Dale_, Apr 29 2017 *)
%Y A179213 Cf. A005117, A045943, A066779, A073837, A179211, A179214.
%K A179213 nonn
%O A179213 1,1
%A A179213 _Reinhard Zumkeller_, Jul 05 2010