Nottinghamshire is a county, not a city, so is covered by several different codes.
The city of Nottingham itself has the area code of 0115 (or +44 115 from outside the UK).
Nottinghamshire - UK Parliament constituency - was created in 1290.
Nottinghamshire - UK Parliament constituency - ended in 1832.
North Nottinghamshire - UK Parliament constituency - was created in 1832.
North Nottinghamshire - UK Parliament constituency - ended in 1885.
All UK area codes begin with a 0. There is no area code 6010 in the UK, and there is no 06010 code either.
The area of Nottinghamshire is 834 sq miles.
UK area code 020 is London.
There is no area code 20 in the UK
There is no 01134 code in the UK.
The country code and area code of Aberdeen, United Kingdom is 44, (0)1224.
Cambridge is in area code 01223, or +44 1223 from outside the UK.
In the UK, 0121 is the area code for Birmingham.