As a repdigit and the product of the two spiritually charged numbers seven and eleven, seventy-seven has a form that number-mystics find attractive, and modern numerology reduces it to five, reading the doubled seven as a heightened call to enquiry before its resolution to change. Beyond the Lamech-and-Matthew pairing, the number carries little developed lore. Its honest core is that scriptural echo, in which the same figure marks both unbounded vengeance and unbounded mercy.
Nicomachus's own arithmetic sorted whole numbers into deficient, perfect and abundant by comparing them with the sum of their own divisors, a genuinely ancient classification that has nothing to do with the letter charts later numerologists built; the modern system that assigns meaning to digit sums is a distinct, twentieth-century construction that happens to borrow the Pythagorean name.
None of this genealogy is hidden by the numerologists themselves: Balliett, Campbell and Jordan each wrote openly as originators and systematisers rather than as transmitters of a secret ancient science, and the chain from Balliett's 1908 book through Campbell's 1931 manual to Jordan's 1965 standardisation is well documented in the numerology literature's own bibliographies.