double factorial
Mathematical term for the product of all integers of the same parity up to a given integer. Used in combinatorics and number theory.
The double factorial represents the product of only odd or only even numbers.
The double factorial of 5 is 5×3×1, which equals 15.
階乗 (factorial) is the product of all positive integers up to n, while 二重階乗 (double factorial) is the product of integers of the same parity.
Compound of 二重 (double) and 階乗 (factorial), a direct translation of the English mathematical term.