OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = A120944(n)^3. - R. J. Mathar, Dec 06 2010
EXAMPLE
216 = 2^3 * 3^3.
9261 = 3^3 * 7^3.
27000 = 2^3 * 3^3 * 5^3.
MAPLE
q:= n-> not isprime(n) and numtheory[issqrfree](n):
map(x-> x^3, select(q, [$4..120]))[]; # Alois P. Heinz, Aug 02 2024
MATHEMATICA
f1[n_]:=Length[Last/@FactorInteger[n]]; f2[n_]:=Union[Last/@FactorInteger[n]]; lst={}; Do[If[f1[n]>1&&f2[n]=={3}, AppendTo[lst, n]], {n, 0, 9!}]; lst
Reap[Do[{p, e}=Transpose[FactorInteger[n]]; If[Length[p]>1 && Union[e]=={3}, Sow[n]], {n, 343000}]][[2, 1]]
PROG
(PARI) [k^3 | k<-[1..100], k>1 && !isprime(k) && issquarefree(k)] \\ Andrew Howroyd, Jan 14 2020
(Python)
from math import isqrt
from sympy import primepi, mobius
def A177493(n):
def f(x): return n+1+primepi(x)+x-sum(mobius(k)*(x//k**2) for k in range(1, isqrt(x)+1))
m, k = n+1, f(n+1)
while m != k:
m, k = k, f(k)
return m**3 # Chai Wah Wu, Aug 02 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, May 10 2010
EXTENSIONS
Definition corrected by R. J. Mathar, Dec 06 2010
Terms a(25) and beyond from Andrew Howroyd, Jan 14 2020
STATUS
approved