Prefix used before counters or nouns to indicate an indefinite small number, e.g. 数人 (several people), 数回 (several times).
数人の学生が質問をした。
Several students asked questions.
I counted the number of participants.
この問題は数回にわたって議論された。
This issue was discussed over several occasions.
Noun or suffix used to refer to a count or amount, often in compounds like 参加者数 (number of participants) or 人口数 (population count).
応募者数は予想を上回った。
The number of applicants exceeded expectations.
この表は年齢別の人口数を示している。
This table shows the population count by age group.
counting; calculation; figures
Refers to the act of counting or the resulting figures; often used in contexts like 数に強い (good with numbers) or 数を数える (to count numbers).
彼は数に強く、暗算が得意だ。
He is good with numbers and skilled at mental arithmetic.
正確な数を出すには時間がかかる。
It takes time to produce accurate figures.
A specific numerical symbol or value; used when talking about numbers as entities, e.g. 数字 (numerals) or 番号 (numbers).
この数は何を表していますか。
What does this number represent?
彼は紙に大きな数を書いた。
He wrote a large number on the paper.
Grammatical term for singular/plural distinction; used in linguistic contexts.
英語の名詞には数の区別がある。
English nouns have a distinction of number.
Literary or idiomatic use referring to one's lot or the course of events; often in set phrases like 数の定め (destiny) or 数奇な運命 (strange fate).
これもまた数の定めというものだろう。
This, too, must be what they call destiny.
彼の数奇な数には誰もが驚いた。
Everyone was surprised by his strange fate.
彼は数に強いので、計算が速い。
He's good with numbers, so he calculates quickly.
The inventory count doesn't add up.
番号 is a number assigned for identification, such as a phone or seat number, whereas 数 refers to number or quantity in a general, abstract sense.
若干 is a more formal, written word meaning "a small, unspecified amount," while 数 as a prefix directly attaches to counters to mean "several."
計算 refers to the act of calculating with numbers, while 数 in this sense refers more broadly to counting or figures themselves.
large number; many · majority
plural; multiple · plural (number)
number of people; head count · many people; large crowd
digit; numeral; numeric character · number; figure; numerical value · a few characters; several written characters
number of times; frequency; count
The kanji 数 is composed of 攵 (action) and 婁 (phonetic, also suggesting repetition), originally meaning 'to count repeatedly'. The reading すう is the Sino-Japanese on'yomi.
function (mathematics) · function (programming)
score; marks; grade · points; score; runs · number of items; number of articles
frequency
number of flat items; sheet count · win-loss difference (sumo)
quantity; amount; volume
index; indicator · exponent
number of days
half the number; half (of an amount) · haploid; haplont
innumerable; countless; myriad
number of long, cylindrical things; count of items counted with 本
number of units; count of machines/vehicles
number of cases; number of items; count
coefficient · coefficient; factor; proportional constant; modulus
variable
majority; more than half
trouble; bother
total number; count
prominent; leading; foremost
number of characters; character count
number of years
arithmetic; elementary school math · calculation; counting
number of copies; circulation