Fifty-one is an odd number. It's divisible by three, which is cool. Numbers that divide by three are my favorites. Yes, I said that. Actually my real favorite numbers are ones with six or more digits when they are found in my checking account. Since that never happens, I'll stick with numbers divisible by three.
Do you all know the easy way to tell if 3 will go into a given number? Add the digits of the number up. If the sum is divisible by three, then the original number is.
5 + 1 = 6
Six is divisible by three, so 51 is divisible by three.
If you can't tell if the sum is divisible by three, keep adding the digits together until you come to a sun that you can tell.
5 + 7 + 8 + 4 + 2 + 4 + 3 + 7 + 2 = 42
Not sure what you've got? Keep going!
4 + 2 = 6
Six is divisible by three, so 578,424,372 is too. And also 42! Isn't it cool?
When I was a kid I used to entertain myself on car trips by seeing if the numbers on billboards, license plates, etc were divisible by three. I still do it sometimes when I'm bored. Once a nerd, always a nerd.
Finally, the source of my fascination with threes. I was a kid in the 70's after all. The part when they start counting by threes gets me every time.
Happy Birthday to me! (I don't think "51st Revolution Around the Sun Completion Day" works in the song. Someone will have to do something about that.)