ei ulykke · accident
Feminine (ei)
Indefinite singular
ei ulykke
Definite singular
ulykka
Indefinite plural
ulykker
Definite plural
ulykkene
Feminine nouns (ei) can always be written with en as well: ei bok, boka or en bok, boken. Both are correct Bokmål.
How to guess the gender Nouns: gender and articles