The said prime minister’s hobby was mathematics:
The kinematic description of ellipses dates from Archimedes and Proclus, as well as the contemporary Claude Mydorge. Johan de Witt describes the hyperbola with a rotating line and a sliding angle, and a parabola by means of a rotating angle and sliding line. In 1661, de Witt’s work appeared in the second volume of von Schooten’s Latin translation of La Géométrie. Elementa Curvarum Linearum has been described as the first textbook in analytic geometry.
De Witt contributed to financial mathematics: The Worth of Life Annuities Compared to Redemption Bonds. This work combined his roles as statesman and as mathematician, and was discussed in the correspondence between Leibniz and Bernoulli concerning the use of probabilities. Ever since the Middle Ages, a life annuity was a way to obtain a regular income from a reliable source. The state, for instance, could provide a widow with a regular income until her death, in exchange for a ‘lump sum’ up front. There were also redemption bonds that were more like a regular state loan. De Witt showed that for the same principal a bond paying 4% interest would result in the same profit as a life annuity of 6% (1 in 17). But the ‘Staten’ at the time were paying over 7% (1 in 14). The publication about life annuities is “one of the first applications of probability in economics.”
https://en.wikipedia.org/wiki/Johan_de_Witt#Disaster_year_and_De_Witt’s_death
