|
|
A346041
|
|
Numbers with exactly 1 semiprime divisor.
|
|
7
|
|
|
4, 6, 8, 9, 10, 14, 15, 16, 21, 22, 25, 26, 27, 32, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57, 58, 62, 64, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 121, 122, 123, 125, 128, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 169
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Numbers of the form p*q or p^k, where p and q are prime and k >= 2.
|
|
LINKS
|
|
|
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
|
|
|
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)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|