The number 70 (seventy) is a significant integer with several distinct properties across mathematics, history, and culture, most notably being the smallest weird number. Here are the key details about 70:
Mathematics: 70 is a composite number, an Erdős–Woods number, a Pell number, and a primitive abundant number.
Weird Number: 70 is the smallest weird number, defined as a natural number that is abundant (the sum of its proper divisors is greater than the number) but not semiperfect (none of its subsets of divisors sum to the number itself).
Representation: In Roman numerals, 70 is represented as LXX. In words, it is written as “seventy”.
Religion & History: The number 70 appears frequently in religious texts, such as the Septuagint (a Greek translation of the Torah often symbolized by LXX) and in various contexts in Islamic history, often representing a large, complete, or indefinite number.
Cannonball Problem: 70 is part of the only nontrivial solution pair to the cannonball problem ( ), along with 24.