It’s a solution for something.
“…the report considers replacement migration for eight low-fertility countries (France, Germany, Italy, Japan, Republic of Korea, Russian Federation, United Kingdom and United States) and two regions (Europe and the European Union).”
IF Germany/Population = 81.41 million (2015) THEN roughly 486,000 replacements are required, according to this.
— Relative to their population size, Italy and Germany would need the largest number of migrants to maintain the size of their working-age populations. Italy would require 6,500 migrants per million inhabitants annually and Germany, 6,000. The United States would require the smallest number — 1,300 migrants per million inhabitants per year.