This week’s Fiddler is a puzzle about adding digits over and over again. For any positive, base-10 integer $n$, define $f(n)$ as the number of times you have to add up its digits until you get a one-digit number. For example, $f(23) = 1$ because $2+3 = 5$, a one-digit number. Meanwhile, $f(888) = 2$, … Continue reading "How many times can you add up the digits?" The post How many times can you add up the digits? first appeared on Book Proofs.
