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 A080398 #18 Feb 20 2022 08:32:39
%S A080398 1,3,2,7,6,6,2,15,13,6,6,14,14,6,6,31,6,39,10,42,2,6,6,30,31,42,10,14,
%T A080398 30,6,2,21,6,6,6,91,38,30,14,30,42,6,22,42,78,6,6,62,57,93,6,14,6,30,
%U A080398 6,30,10,30,30,42,62,6,26,127,42,6,34,42,6,6,6,195,74,114,62,70,6,42,10
%N A080398 Largest squarefree number dividing sum of divisors of n.
%C A080398 Not multiplicative, but satisfies a similar condition: For all coprime x, y (with gcd(x,y)=1), a(x*y) = LCM(a(x), a(y)), where LCM is the least common multiply of its arguments, A003990. Compare also with A351560. - _Antti Karttunen_, Feb 20 2022
%H A080398 Antti Karttunen, <a href="/A080398/b080398.txt">Table of n, a(n) for n = 1..16384</a>
%H A080398 <a href="/index/Lc#lcm">Index entries for sequences related to lcm's</a>
%H A080398 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A080398 a(n) = A007947(A000203(n)).
%F A080398 a(n) = A019565(A351560(n)). - _Antti Karttunen_, Feb 20 2022
%e A080398 n=12:sigma[12]=1+2+3+4+6+12=28, sqf-kernel=14=a(12)
%t A080398 ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] cor[x_] := Apply[Times, ba[x]] Table[cor[DivisorSigma[1, w]], {w, 1, 100}]
%o A080398 (PARI) a(n) = factorback(factor(sigma(n))[,1]); \\ _Michel Marcus_, Nov 18 2017
%Y A080398 Cf. A000203, A007947, A019565, A351560.
%K A080398 nonn
%O A080398 1,2
%A A080398 _Labos Elemer_, Mar 19 2003