I dreamed about the date 18.v.1638 (May 18, 1638) last night.
As I currently do research on odd perfect numbers, and because Rene Descartes lived during the years 1596 to 1650, and as I am not a math historian, I would like to ask the experts here:
Did Rene Descartes send or receive any letters (regarding mathematics) on 18.v.1638 (May 18, 1638)?
I tried searching via Google, using the keywords Descartes and 18.v.1638, but there are too many search results (with none of them promising). I did skim through a few of them, but did not find any letters on mathematics sent to or received by Descartes on May 18, 1638.