OFFSET
1,4
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Rafael Jakimczuk and Matilde Lalín, The Number of Prime Factors on Average in Certain Integer Sequences, Journal of Integer Sequences, Vol. 25 (2022), Article 22.2.3.
FORMULA
MATHEMATICA
f[n_] := Module[{e = FactorInteger[n][[;; , 2]]}, If[AllTrue[e, # < 3 &], Total[e], Nothing]]; f[1] = 0; Array[f, 100]
PROG
(PARI) lista(max) = {my(e); for(k = 1, max, e = factor(k)[, 2]; if(k == 1 || vecmax(e) < 3, print1(vecsum(e), ", "))); }
(Python)
from sympy import mobius, integer_nthroot, primeomega
def A368779(n):
def f(x): return n+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 primeomega(m) # Chai Wah Wu, Aug 06 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Amiram Eldar, Jan 05 2024
STATUS
approved