niàn
twenty (20), in a limited number of set expressions
also written using banker's character 念
niàn sì shǐ
twenty four dynastic histories (or 25 or 26 in modern editions)
same as 二十四史[Er4 shi2 si4 Shi3]
niàn bā chán
the twenty-eight constellations
also written 二十八宿[er4 shi2 ba1 xiu4]