OFFSET
1,1
COMMENTS
Numbers of the form p*q or p^k, where p and q are prime and k >= 2.
Numbers k such that A086971(k) = 1. - Wesley Ivan Hurt, Jun 21 2024
EXAMPLE
6 is in the sequence since it has exactly 1 semiprime divisor, namely 6.
16 is in the sequence since it has exactly 1 semiprime divisor, namely 4.
MATHEMATICA
Select[Range@200, Length@Select[Divisors@#, PrimeOmega@#==2&]==1&] (* Giorgos Kalogeropoulos, Jul 03 2021 *)
PROG
(PARI) isok(k) = sumdiv(k, d, bigomega(d)==2) == 1; \\ Michel Marcus, Jul 03 2021
(Python)
from sympy import factorint
def ok(n):
f = factorint(n); w = len(f); W = sum(f.values())
return (w == 1 and W >= 2) or (w == 2 and W == 2)
print(list(filter(ok, range(170)))) # Michael S. Branicky, Jul 03 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Jul 02 2021
STATUS
approved