1666 AD resides in the 17th century. Unless the year ends in -00, you can add 1 to the first number if it is a three digit year and 1 to the first two numbers if it is a four digit year.
For example, 411 AD is in the 5th century. This is a 3 digit year so take the first number, (4) and add (1), 4+1=5th Century.
The first century AD
The sixth century AD covers the years from 501 AD to 600 AD.
-99
Any year between 1501 AD and 1600 AD - including 1537 - is in the sixteenth century.
20th century.
The 17th Century AD - it happened in 1666.
1666 is in the 17th century.
17th Century
The 1st century AD.
It is the 18th century AD.
The first century AD.
It is the first century AD.
The 1st century AD.
1st century AD
It is the second century AD.
The 1st century AD.
It is the first century AD.