Seventy-seven is seven times eleven and reduces to fourteen and then five. Its scriptural weight lies in a pair of linked passages about vengeance and forgiveness. In Genesis, Lamech boasts that if Cain is avenged sevenfold, then Lamech seventy-sevenfold, an escalation of blood-vengeance. In the Gospel of Matthew, Jesus reverses the figure: asked how often one must forgive, he answers not seven times but seventy-seven times, in the reading many translations prefer, deliberately overturning Lamech's boast so that limitless forgiveness answers limitless revenge. The Greek can also be rendered seventy times seven, four hundred and ninety, and the ambiguity is genuine.
In chemistry, seventy-seven is the atomic number of iridium, named from the Latin iris, rainbow, for the vivid range of colours in its salts, and discovered by Smithson Tennant in 1803. A thin, worldwide layer of iridium-enriched clay marks the boundary between the Cretaceous and Paleogene periods and anchors the Alvarez hypothesis that an asteroid impact ended the age of the dinosaurs.
Seventy-seven factors as 7 x 11 and carries 4 divisors in all. Summing its proper divisors gives only 19, short of the number itself, which places it among the deficient numbers in the same classical scheme.