It's +45 for all of Denmark, with an 8-digit subscriber number.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
Denmark does not use city or area codes, it just has eight-digit telephone numbers. From outside Denmark, prefix the country code +45
Leichtenstein is telephone country code +423.
There is no area code +1 453 in North America. International country code +45 is Denmark.
where is telephone country code 1816
That is not a country code.
Fiji has telephone country code +679.
Country code +57 is Colombia.
Gibraltar is country code +350.
Moldova is country code +373.
Slovenia is country code +386.
Vanuatu is country code +678.
Niue is country code +683.