NOUNS
Danish nouns are either common gender (en- words) or neuter gender
(et- words). The corresponding indefinite article is en or et, ‘a(n)’.
INDEFINITE
Common gender
en mand (a man)
en uge (a week)

Neuter gender
et hus (a house)
et æble
(an apple)

Gender determines the form with end article (definite article) singular:
DEFINITE
Common gender

manden (the man)
ugen (the week)

Neuter gender
huset (the house)
æblet (the apple)

Reference: Danish an Essencial Grammar (Tom Lundskær-Nielsen and Philip Holmes), 2ed.