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 A382904 #7 Apr 09 2025 04:19:39
%S A382904 1,2,3,2,5,6,7,2,3,10,11,6,13,14,15,17,6,19,10,21,22,23,6,5,26,3,14,
%T A382904 29,30,31,33,34,35,6,37,38,39,10,41,42,43,22,15,46,47,7,10,51,26,53,6,
%U A382904 55,14,57,58,59,30,61,62,21,65,66,67,34,69,70,71,6,73,74
%N A382904 The squarefree kernel of the n-th biquadratefree number.
%H A382904 Amiram Eldar, <a href="/A382904/b382904.txt">Table of n, a(n) for n = 1..10000</a>
%F A382904 a(n) = A007947(A046100(n)).
%F A382904 Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = zeta(4)^2 * Product_{p prime} (1 - 1/p^2 + 1/p^3 - 1/p^4 + 1/p^5 - 1/p^6) = 0.8197259315983831456004... .
%t A382904 s[n_] := Module[{fct = FactorInteger[n]}, If[AllTrue[fct[[;; , 2]], # < 4 &], Times @@ fct[[;;, 1]], Nothing]]; Array[s, 100]
%o A382904 (PARI) list(lim) = {my(f); print1(1, ", "); for(k = 2, lim, f = factor(k); if(vecmax(f[, 2]) < 4, print1(vecprod(f[, 1]), ", ")));}
%Y A382904 Cf. A007947, A013662, A046100.
%Y A382904 Similar sequences: A382902, A382903, A382905, A382906.
%K A382904 nonn,easy
%O A382904 1,2
%A A382904 _Amiram Eldar_, Apr 08 2025