Commonly, a binomial coefficient is indexed by a pair of integers n ≥ k ≥ 0 and is written as " - quoted from Wikipedia.
ໂດຍທົ່ວໄປແລ້ວ, ຕົວຄູນ binomial ແມ່ນຖືກດັດສະນີໂດຍຄູ່ ຈໍາ ນວນ n ≥ k ≥ 0 ແລະຖືກຂຽນເປັນ" - ອ້າງອີງຈາກ Wikipedia.