<span>"Prime" redirects here. For other uses, see Prime (disambiguation).
Demonstration, with Cuisenaire rods, that the number 7 is prime, being divisible only by 1 and 7
A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example, 5 is prime because 1 and 5 are its only positive integer factors, whereas 6 is composite because it has the divisors 2 and 3 in addition to 1 and 6. The fundamental theorem of arithmetic establishes the central role of primes in number theory: any integer greater than 1 is either a prime itself or can be expressed as a product of primes that is unique up to ordering. The uniqueness in this theorem requires excluding 1 as a prime because one can include arbitrarily many instances of 1 in any factorization, e.g., 3, 1 · 3, 1 · 1 · 3, etc. are all valid factorizations of 3.</span>
The prime numbers from 2 to 61, inclusive, are 2<span>, </span>3<span>, </span>5<span>, </span>7<span>, </span>11<span>, </span>13<span>, 17, 19, 23, </span>29<span>, </span>31<span>, </span>37<span>, </span>41<span>, 43, 47, 53, 59, and 61
That's 18 numbers total (you can do the counting to check).
