1243

1243 is the natural number that comes after 1242 and before 1244. It is an odd composite number. Its prime factorization is 11 × 113, so it is a semiprime and square-free.

In various numeral systems, it is written as MCCXLIII in Roman numerals; in binary it is 10011011011; in hexadecimal 0x4DB; in octal 2333. The decimal digits are 1, 2, 4, and 3, which sum to 10; the digital root is 1.

In the year 1243 CE, notable events included the Battle of Köse Dağ, where Mongol forces under Baiju Noyan defeated the Seljuk Sultanate of Rum near Köse Dağ in Anatolia, resulting in Mongol suzerainty over much of Anatolia and a weakening of the Rum Sultanate. This year is part of the broader period of Mongol expansion in the Middle East and eastern Europe, influencing political and military dynamics across the region.