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A377880
Nonprime cubefree numbers.
1
1, 4, 6, 9, 10, 12, 14, 15, 18, 20, 21, 22, 25, 26, 28, 30, 33, 34, 35, 36, 38, 39, 42, 44, 45, 46, 49, 50, 51, 52, 55, 57, 58, 60, 62, 63, 65, 66, 68, 69, 70, 74, 75, 76, 77, 78, 82, 84, 85, 86, 87, 90, 91, 92, 93, 94, 95, 98, 99, 100, 102, 105, 106, 110, 111
OFFSET
1,2
MAPLE
q:= n-> not isprime(n) and andmap(i-> i[2]<3, ifactors(n)[2]):
select(q, [$1..111])[]; # Alois P. Heinz, Nov 10 2024
MATHEMATICA
Select[Range[120], !PrimeQ[#] && Max[FactorInteger[#][[;; , 2]]] < 3 &] (* Amiram Eldar, Nov 10 2024 *)
PROG
(Python)
from sympy import primepi, mobius, integer_nthroot
def A377880(n):
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)))
m, k = n, f(n)
while m != k: m, k = k, f(k)
return m # Chai Wah Wu, Nov 13 2024
CROSSREFS
Intersection of A004709 and A018252.
Cf. A000469.
Sequence in context: A277494 A174896 A304634 * A375962 A319240 A331051
KEYWORD
nonn
AUTHOR
Sahil K. Das, Nov 10 2024
STATUS
approved