Twenty-eight is a perfect number, equal to the sum of its proper divisors, one, two, four, seven and fourteen, a property it shares with six and then with no number below it in the hundreds. The Greek mathematicians prized such numbers, and Augustine took the perfection of six and twenty-eight as a sign that God had ordered creation by number, remarking that God made the world in six days because six is perfect, not the reverse. Twenty-eight is also triangular, the sum of the numbers one through seven, and it approximates the length of a lunar month, which is why the moon's circuit is often given as twenty-eight days and the lunar mansions of the Chinese and Arabic astronomers were counted as twenty-eight, the xiu and the manazil respectively.
Cheiro's 1926 Book of Numbers reads twenty-eight as a compound full of contradictions, a person of great promise whose gains are lost again unless carefully provided for, warning of loss through misplaced trust, opposition in trade and the danger of loss through law; the reading sits in an odd counterpoint to the number's strict mathematical perfection already described above, one tradition finding twenty-eight complete and self-sufficient, the other finding it precarious and easily undone, arrived at by entirely unrelated methods centuries apart.