#math trivia for #February14: 45 is the 9th triangular number: 45 = 1+2+3+…+9. How do you make a 9×9 square out of 45-unit triangles? — Burt Kaliski Jr. (@modulomathy) February 15, 2012 The nth triangular number has the form 1+2+3+…+n, and is so named because it measures the “units” in a triangularly shaped figure with … Continue reading