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 A002734 M0611 N0222 #29 Jun 09 2025 00:35:04
%S A002734 2,3,5,6,7,2,10,11,3,13,14,15,17,2,19,5,21,22,23,6,26,3,7,29,30,31,2,
%T A002734 33,34,35,37,38,39,10,41,42,43,11,5,46,47,3,2,51,13,53,6,55,14,57,58,
%U A002734 59,15,61,62,7,65,66,67,17,69,70,71,2,73,74,3,19,77,78,79
%N A002734 Remove squares!
%C A002734 This is a riddle. (Explanation: This lists the squarefree part of the nonsquares. - _Amiram Eldar_, Sep 05 2020)
%C A002734 A007913 with the ones removed.
%D A002734 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A002734 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A002734 Amiram Eldar, <a href="/A002734/b002734.txt">Table of n, a(n) for n = 1..10000</a>
%H A002734 H. Brocard, <a href="https://gdz.sub.uni-goettingen.de/id/PPN598948236_0004?tify={%22pages%22:[187],%22view%22:%22info%22}">Notes élémentaires sur le problème de Peel</a>, Nouvelle Correspondance Mathématique, Vol. 4 (1878), pp. 161-169.
%F A002734 a(n) = A007913(A000037(n)). - _Amiram Eldar_, Sep 05 2020
%F A002734 Sum_{k=1..n} a(k) ~ c * n^2, where c = Pi^2/30 = 0.328986... . - _Amiram Eldar_, Feb 02 2024
%t A002734 core[n_] := Times @@ (First[#]^Mod[Last[#], 2] & /@ FactorInteger[n]); Select[core /@ Range[100], # > 1 &] (* _Amiram Eldar_, Sep 05 2020 *)
%o A002734 (Python)
%o A002734 from math import isqrt, prod
%o A002734 from sympy import factorint
%o A002734 def A002734(n):
%o A002734 k = isqrt(n)
%o A002734 return prod(p for p, e in factorint(n+k+int(n>k*(k+1))).items() if e&1) # _Chai Wah Wu_, Jun 05 2025
%Y A002734 Intersection of A000037 and A007913.
%K A002734 nonn
%O A002734 1,1
%A A002734 _N. J. A. Sloane_