Last Updated：2025/11/27
(mathematics, combinatorics) For an odd integer, the result of multiplying all the odd integers from 1 to the given number; or for an even integer, the result of multiplying all the even integers from 2 to the given number; symbolised by a double exclamation mark (!!). For example, 9!! = 1 × 3 × 5 × 7 × 9 = 945.
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double factorial
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Source Word
double factorial
Noun
(mathematics,
combinatorics)
For
an
odd
integer,
the
result
of
multiplying
all
the
odd
integers
from
1
to
the
given
number;
or
for
an
even
integer,
the
result
of
multiplying
all
the
even
integers
from
2
to
the
given
number;
symbolised
by
a
double
exclamation
mark
(!!).
For
example,
9!!
=
1
×
3
×
5
×
7
×
9
=
945.
Japanese Meaning
二重階乗：数学や組み合わせ論において、奇数の場合は1からその数までのすべての奇数の積、偶数の場合は2からその数までのすべての偶数の積を計算する演算。記号「!!」で表される。
Sense（1）
(mathematics,
combinatorics)
For
an
odd
integer,
the
result
of
multiplying
all
the
odd
integers
from
1
to
the
given
number;
or
for
an
even
integer,
the
result
of
multiplying
all
the
even
integers
from
2
to
the
given
number;
symbolised
by
a
double
exclamation
mark
(!!).
For
example,
9!!
=
1
×
3
×
5
×
7
×
9
=
945.
（ plural ）
