How many neutrons does an atom of dubnium have in its nucleus

Dubnium is a synthetic element ... Number 105.  It can be created
in a laboratory but it's not found in nature.

Fifteen (15) different isotopes of Dubnium have been created.  They all
have 105 protons in the nucleus of every atom, but they have anywhere
from 256 to 270 neutrons in each nucleus.

The most stable isotope of Dubnium is  ²⁶⁸Db , with 163 neutrons in the
nucleus.  That form of Dubnium atom has a 50-50 chance of surviving
for around 28 hours before it falls apart.