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 A072778 #8 Aug 19 2024 11:39:10 %S A072778 1,2,3,4,5,6,7,8,9,10,11,11,12,13,14,15,16,16,17,17,18,19,20,20,21,22, %T A072778 23,23,24,25,26,27,28,29,30,31,32,33,34,34,35,36,37,37,37,38,39,39,40, %U A072778 40,41,41,42,42,43,43,44,45,46,46,47,48,48,49,50,51,52,52,53,54,55,55 %N A072778 Number of powers of squarefree numbers <= n. %o A072778 (Python) %o A072778 from math import isqrt %o A072778 from sympy import mobius, integer_nthroot %o A072778 def A072778(n): %o A072778 def f(x): return int(sum(mobius(k)*(x//k**2) for k in range(1, isqrt(x)+1))) %o A072778 return 2-(m:=n.bit_length())+sum(f(integer_nthroot(n,k)[0]) for k in range(1,m)) # _Chai Wah Wu_, Aug 19 2024 %Y A072778 Cf. A072774, A013928. %K A072778 nonn %O A072778 1,2 %A A072778 _Reinhard Zumkeller_, Jul 10 2002