648

648 is the natural number that comes after 647 and before 649. It is an even composite number. Its prime factorization is 2^3 × 3^4, giving 20 positive divisors: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 27, 36, 54, 72, 81, 108, 162, 216, 324, and 648. In base 10 it is a Harshad number since 6+4+8=18 and 648/18=36. The digit sum is 18, a multiple of 9, so 648 is divisible by 9 and by 3.

In numeral systems, 648 is written as DCXLVIII in Roman numerals. In other bases, it is 1210_8 in base 8, 1614_7 in base 7, and 800_9 in base 9. In binary, 648 equals 1010001000_2.

As a year, 648 CE is a year in the 7th century. In global chronology, it falls within late antiquity, a period marked by the expansion of the Islamic Caliphate and the continuation of Byzantine and Persian empires.