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 A083730 #19 Feb 11 2021 03:31:55
%S A083730 1,1,1,4,1,1,1,4,9,1,1,4,1,1,1,4,1,9,1,4,1,1,1,4,25,1,9,4,1,1,1,4,1,1,
%T A083730 1,9,1,1,1,4,1,1,1,4,9,1,1,4,49,25,1,4,1,9,1,4,1,1,1,4,1,1,9,4,1,1,1,
%U A083730 4,1,1,1,9,1,1,25,4,1,1,1,4,9,1,1,4,1,1,1,4,1,9,1,4,1,1,1,4,1,49,9
%N A083730 Greatest prime^2 factor of n, or a(n)=1 for squarefree n.
%C A083730 Not multiplicative, for example a(4)*a(9) <> a(36). - _R. J. Mathar_, Oct 31 2011
%H A083730 Charles R Greathouse IV, <a href="/A083730/b083730.txt">Table of n, a(n) for n = 1..10000</a>
%F A083730 a(n) = A249740(n)^2. - _Amiram Eldar_, Feb 11 2021
%t A083730 a[n_] := If[(pos = Position[(f = FactorInteger[n])[[;; , 2]], _?(# >= 2 &)]) == {}, 1, f[[pos[[-1, 1]], 1]]^2]; Array[a, 100] (* _Amiram Eldar_, Nov 14 2020 *)
%o A083730 (PARI) a(n)=my(f=factor(n)); forstep(i=#f~,1,-1, if(f[i,2]>1, return(f[i,1]^2))); 1 \\ _Charles R Greathouse IV_, Jul 23 2017
%Y A083730 Cf. A006530, A001248, A005117, A013929, A008833, A046028, A249740.
%K A083730 nonn,easy
%O A083730 1,4
%A A083730 _Reinhard Zumkeller_, Jun 14 2003