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 A053165 #36 Aug 20 2021 08:15:54
%S A053165 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,1,17,18,19,20,21,22,23,24,25,26,
%T A053165 27,28,29,30,31,2,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,3,49,
%U A053165 50,51,52,53,54,55,56,57,58,59,60,61,62,63,4,65,66,67,68,69,70,71,72,73
%N A053165 4th-power-free part of n.
%H A053165 Chai Wah Wu, <a href="/A053165/b053165.txt">Table of n, a(n) for n = 1..10000</a>
%H A053165 Henry Bottomley, <a href="http://fs.gallup.unm.edu/Bottomley-Sm-Mult-Functions.htm">Some Smarandache-type multiplicative sequences</a>.
%F A053165 a(n) = n/A008835(n).
%F A053165 Dirichlet g.f.: zeta(4s)*zeta(s-1)/zeta(4s-4). The Dirichlet convolution of this sequence with A008835 is A000203. - _R. J. Mathar_, Apr 05 2011
%F A053165 From _Peter Munn_, Jan 15 2020: (Start)
%F A053165 a(2) = 2; a(4) = 4; a(n^4) = 1; a(A003961(n)) = A003961(a(n)); a(A059897(n,k)) = A059897(a(n), a(k)).
%F A053165 a(A225546(n)) = A225546(A065331(n)).
%F A053165 (End)
%F A053165 Multiplicative with a(p^e) = p^(e mod 4). - _Amiram Eldar_, Sep 07 2020
%F A053165 Sum_{k=1..n} a(k) ~ Pi^4 * n^2 / 210. - _Vaclav Kotesovec_, Aug 20 2021
%t A053165 f[p_, e_] := p^Mod[e, 4]; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* _Amiram Eldar_, Sep 07 2020 *)
%o A053165 (Python)
%o A053165 from operator import mul
%o A053165 from functools import reduce
%o A053165 from sympy import factorint
%o A053165 def A053165(n):
%o A053165 return 1 if n <=1 else reduce(mul,[p**(e % 4) for p,e in factorint(n).items()])
%o A053165 # _Chai Wah Wu_, Feb 04 2015
%o A053165 (PARI) a(n)=my(f=factor(n)); f[,2]=f[,2]%4; factorback(f) \\ _Charles R Greathouse IV_, Sep 02 2015
%Y A053165 Equivalent sequences for other powers: A007913 (2), A050985 (3).
%Y A053165 Cf. A000190, A000203, A008835.
%Y A053165 A003961, A059897 are used to express relationship between terms of this sequence.
%Y A053165 Related to A065331 via A225546.
%K A053165 nonn,mult
%O A053165 1,2
%A A053165 _Henry Bottomley_, Feb 29 2000