Mendeleev's predicted elements
Dmitri Mendeleev published a periodic table of the chemical elements in 1869 based on properties that appeared with some regularity as he laid out the elements from lightest to heaviest. When Mendeleev proposed his periodic table, he noted gaps in the table and predicted that as-then-unknown elements existed with properties appropriate to fill those gaps. He named them eka-boron, eka-aluminium and eka-silicon with atomic masses 44, 68 and 72 respectively.
Dionysius Exiguus' Easter table
Dionysius Exiguus's Easter table was constructed in the year 525 by Dionysius Exiguus for the years 532–626. He obtained it from an Easter table attributed to Patriarch Cyril of Alexandria for the years 437–531. The latter was constructed around the year 440 by means of extrapolation from an Alexandrian Easter table constructed around the year 390 by Patriarch Theophilus of Alexandria. The great historical importance of Dionysius' Easter table is twofold: