Seventh son of a seventh son

The seventh son of a seventh son is a concept from folklore regarding special powers given to, or held by, such a son. To qualify as "the seventh son of a seventh son", one must be the seventh male child born in an unbroken line with no female siblings born between, and to a father who himself is the seventh male child born in an unbroken line with no female siblings born between. In some beliefs, the special powers are inborn, inherited simply by virtue of his birth order; in others, the powers are granted to him by God or the gods because of his birth order. In many cases, seventh sons who are not born to a seventh son are also said to have supernatural or healing abilities.

The number seven has a long history of mystical and biblical significance, such as seven virtues, seven deadly sins, Seven Sleepers and Seven Heavens. The number seven had mystical and religious significance in Mesopotamian culture by the 22nd century BCE at the latest. This was likely because in the Sumerian sexagesimal number system, dividing by seven was the first division which resulted in infinitely repeating fractions.