The year 2013 may have looked unlucky with that 13 on the end, but it turned out to be a great number. It was the first year in a long time with 4 different digits. Also, the number 13 is prime, meaning it’s divisible only by itself and 1, and can’t be split into other equal-sized groups, so 2013 looks kind of yucky and prime also. But you can actually divide a lot of numbers into it. Let’s do the math to find them!
Wee ones: Of the digits 2, 0, 1 and 3, which one is biggest?
Little kids: Numbers whose digits add up to a multiple of 3 are divisible by 3 (you can add 3 over and over to get that total). What do 2013’s digits add up to, and is it divisible by 3? Bonus: How old were you in 2013, if you’d already been born?
Big kids: We hadn’t had a year with 4 different digits in a long time. When was the last one before that? Bonus: Years with 4 different digits are actually pretty common. Before 1987, what was the last year that repeated any digits?
Wee ones: 3 is biggest.
Little kids: Yes! They add to 6, which is divisible 3 (=3 + 3). Bonus: Different for everyone…take your age today, then subtract the number of years passed since 2013. Example: if you’re doing this in 2016, 2013 was 3 years ago.
Big kids: 1987. Bonus: 1981. Year 1982-1987 all had 4 different digits.
And thank you to Lynn Salvo at MathTree for the great 2013 factoids!