 The total number of grains equals 18,446,744,073,709,551,615 (eighteen quintillion four hundred and forty-six quadrillion seven hundred and forty-four trillion seventy-three billion seven hundred and nine million five hundred and fifty-one thousand six hundred and fifteen)—about 2,000 times annual world production—much more than most expect.This exercise can be used to demonstrate how quickly exponential sequences grow, as well as to introduce exponents, zero power, capital-sigma notation and geometric series.Updated for modern times using pennies and a hypothetical question such as "Would you rather have a million dollars or a penny on day one, doubled every day until day 30?