Day 165/365 #FactsOfTheDay
1️⃣6️⃣5️⃣ = the 9th tetrahedral number, (meaning it represents a pyramid with a triangular base).
On this day in;
🩸 2004 #WorldBloodDonorDay was first organised by the WHO.
💔 1940 Auschwitz concentration camp started operation.
🪵 1834 Isaac Fischer Jr. patented sandpaper.
