noun
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.
二重階乗は、奇数のみ、または偶数のみの積を表す。
The double factorial represents the product of only odd or only even numbers.
5の二重階乗は5×3×1で15になる。
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.