651

651 is a natural number that follows 650 and precedes 652. It is an odd composite number with prime factorization 3 × 7 × 31. Because it is a product of distinct primes, 651 is squarefree. Its divisors are 1, 3, 7, 21, 31, 93, 217, and 651.

In different representations, 651 in base 2 is 1010001011, and in Roman numerals it is DCLI.

In mathematics, the factorization 3 × 7 × 31 shows that 651 is squarefree and composite. The sum of its digits is 12, so the number is divisible by 3 but not by 9; indeed, 651 ÷ 3 = 217, which equals 7 × 31.

In the calendar, the year 651 CE saw the continued rise of the early Islamic caliphates and the decline of the Sassanian Empire, with Yazdegerd III’s death marking the end of that dynasty. Traditions associated with this period also place the standardization or compilation of the Qur’an under Caliph Uthman around this time, though exact dating varies among sources.

In modern usage, 651 is the area code for the eastern portion of Minnesota, including Saint Paul, within the North American Numbering Plan. It is used for telephone numbering in that region.