In math, pi is a constant. The dependable number, best shortened to 3.14159, is an all-star champ, frequently showing up in formulas throughout mathematics and physics. Every year geeks and other smart people celebrate this useful number, fittingly, on March 14. But you don’t have to be a numbers expert to score holiday deals. The Herbivorous Butcher will host a pie-filled pop-up with vegan treats from 4 to 6 p.m. Stop in for a $3 slice, or pre-order an entire pie for $20. Varieties include key lime, strawberry Pop Tart, banana split, and grasshopper.