in late Middle English a and an commonly were written as one word with the following noun, which caused confusion over how such words ought to be divided. In nickname, newt, and British dialectal naunt, the -n- belongs to a preceding indefinite article an or possessive pronoun mine.
Other examples of this from Middle English manuscripts include a neilond ("an island," early 13c.), a narawe ("an arrow," c. 1400), a nox ("an ox," c. 1400), a noke ("an oak," early 15c.), a nappyle ("an apple," early 15c.), a negge ("an egg," 15c.). My naunt for mine aunt is recorded from 13c.-17c. Natomy or atomy was common in Elizabethan English for anatomy. In 16c., an idiot sometimes became a nidiot, which, with still-common casual pronunciation, became nidget, which, alas, has not survived. Marlowe (1590) has Natolian for Anatolian.
The process also worked in surnames, from oblique cases of Old English at "by, near," as in Nock/Nokes/Noaks from atten Oke "by the oak;" Nye from atten ye "near the lowland;" and see Nashville. A manuscript from c. 1500 has a nylle for "an isle."
But it is more common for an English word to lose an -n- to a preceding a: apron, auger, adder, umpire, humble pie, etc. The mathematical use of n for "an indefinite number" is first recorded 1852, in to the nth power.