+"603" most commonly refers to the [area code](/wiki/Area_code) serving the entire state of New Hampshire in the United States, a numeric assignment for [telecommunications](/wiki/Telecommunications). As a natural number, it follows 602 and precedes 604.
+## See also
+- [New Hampshire](/wiki/New_Hampshire)
+- [Number](/wiki/Number)
+- [Number Theory](/wiki/Number_Theory)
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