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 A377880 #23 Nov 14 2024 02:11:21 %S A377880 1,4,6,9,10,12,14,15,18,20,21,22,25,26,28,30,33,34,35,36,38,39,42,44, %T A377880 45,46,49,50,51,52,55,57,58,60,62,63,65,66,68,69,70,74,75,76,77,78,82, %U A377880 84,85,86,87,90,91,92,93,94,95,98,99,100,102,105,106,110,111 %N A377880 Nonprime cubefree numbers. %p A377880 q:= n-> not isprime(n) and andmap(i-> i[2]<3, ifactors(n)[2]): %p A377880 select(q, [$1..111])[]; # _Alois P. Heinz_, Nov 10 2024 %t A377880 Select[Range[120], !PrimeQ[#] && Max[FactorInteger[#][[;; , 2]]] < 3 &] (* _Amiram Eldar_, Nov 10 2024 *) %o A377880 (Python) %o A377880 from sympy import primepi, mobius, integer_nthroot %o A377880 def A377880(n): %o A377880 def f(x): return int(n+x+primepi(x)-sum(mobius(k)*(x//k**3) for k in range(1, integer_nthroot(x,3)[0]+1))) %o A377880 m, k = n, f(n) %o A377880 while m != k: m, k = k, f(k) %o A377880 return m # _Chai Wah Wu_, Nov 13 2024 %Y A377880 Intersection of A004709 and A018252. %Y A377880 Cf. A000469. %K A377880 nonn %O A377880 1,2 %A A377880 _Sahil K. Das_, Nov 10 2024