Overview
1221 is an ordinary four-digit integer and a commonly encountered calendar year. As a number it sits between 1220 and 1222; as a year it may be referenced in both Common Era (AD 1221) and before the Common Era (1221 BC) contexts. The figure appears in mathematics, chronology and as an identifier for products, roads, and records.
Mathematical characteristics
In base 10, 1221 is a palindrome: it reads the same forward and backward. It is a composite odd number with the prime factorization 3 × 11 × 37. From that factorization follows the complete list of positive divisors: 1, 3, 11, 33, 37, 111, 407 and 1221. Because it is composite it is neither prime nor a perfect power.
- Roman numeral: MCCXXI
- Binary: 10011000101₂
- Hexadecimal: 4C5₁₆
- Octal: 2305₈
- Digit sum: 1+2+2+1 = 6 (digital root 6)
Notable numerical facts
1221 exemplifies a simple divisibility observation: any even-digit palindrome in base 10 is divisible by 11. That follows from the alternating-sum test used for 11: for 1221 the alternating sum is 1−2+2−1 = 0, which shows 11 divides it. The number is near the perfect square 35² = 1225, but it is not itself a square.
Historical and calendrical context
When treated as a year, 1221 (MCCXXI) is part of the early 13th century. Events and movements from that period are discussed in histories of medieval Europe, the Middle East and Asia—contexts include political changes, religious orders, and the expansion of empires. Exact events are the subject of historical sources specific to each region and should be consulted for detail.
Uses and occurrences
As with many four-digit numerals, 1221 commonly appears as an identifier: in addresses, model numbers, catalogue entries, statutes, and route numbers. Its palindromic form also makes it a choice for stylized branding or memorable codes. Mathematicians study it as a simple composite example and use it to illustrate factorization and divisibility rules.