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 A375245 #25 Aug 10 2024 21:39:14
%S A375245 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,15,16,17,18,19,20,21,22,23,24,25,
%T A375245 26,27,28,29,30,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,45,46,
%U A375245 47,48,49,50,51,52,53,54,55,56,57,58,59,60,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,75,75,76,77,78,79
%N A375245 Number of biquadratefree numbers <= n.
%C A375245 First differs from A309083 at n = 81: a(81) = 75, A309083(n) = 77. - _Andrew Howroyd_, Aug 10 2024
%H A375245 Andrew Howroyd, <a href="/A375245/b375245.txt">Table of n, a(n) for n = 1..10000</a>
%F A375245 a(n) = Sum_{d>=1} mu(d)*floor(n/d^4), where mu is the Moebius function A008683.
%F A375245 n/a(n) converges to zeta(4).
%F A375245 a(n) = Sum_{k = 1..n} A307430(k).
%t A375245 Accumulate[Table[Boole[Max[FactorInteger[n][[;; , 2]]] < 4], {n, 1, 100}]] (* _Amiram Eldar_, Aug 10 2024 *)
%o A375245 (Python)
%o A375245 from sympy import mobius, integer_nthroot
%o A375245 def A375245(n): return int(sum(mobius(k)*(n//k**4) for k in range(1, integer_nthroot(n,4)[0]+1)))
%o A375245 (PARI) a(n) = sum(d=1, sqrtnint(n,4), moebius(d)*(n\d^4)) \\ _Andrew Howroyd_, Aug 10 2024
%Y A375245 Cf. A060431, A013662, A046100, A215267, A307430.
%K A375245 nonn,easy
%O A375245 1,2
%A A375245 _Chai Wah Wu_, Aug 07 2024
%E A375245 a(68) onwards from _Andrew Howroyd_, Aug 10 2024