古代中国から伝わった陰陽道の考え方によると、 数では奇数が陽で偶数が陰であり、そのため日本では奇数は縁起が良いという考えがあります。おそらくこれが理由で日本のお城や塔は奇数の階層になっているものが多いです。
なお、奇数は割れない、別れないという理由で、結婚式などのご祝儀の金額として使われることも多いです。
According to the Ying and Yang way of thinking passed down from Ancient China, odd numbers are considered positive and even numbers as negative. This is why in Japan, odd numbers are known to bring good luck. This is often known as the reason to why many Japanese castles and towers have an odd number of steps in staircases.
Additionally, due to the nature of an odd number which cannot be divided equally or undivided and cannot be separated, its commonly used as the appropriate amount of money to offer as a celebration gift at Japanese weddings.
