What's special about this number

Here's a website for the inquiring mind
Like who knew 9973 is the largest 4-digit prime?

ps. that was a rhetorical question, I'm not actually asking who knew :op

All Right Prime Numbers - a personal obsession of mine for over 30 years - the best site for primes can be found here
I even have a couple entries under prime curios under "GUST" for numbers 3 and 5

:) Prime numbers are fun. I did a program that figured out all the prime numbes I had it go to 100 000 000 found all the prime numbes & listed them.. took about 70 seconds to run.
I wonder if I could write up the same program now. i just did it in my head in about 5 minutes.

Pick any number.

Add all the digits together.

Then add the digits of that number together.

Keep doing this until you have a single digit.

If that number is nine, your original number is evenly divisible by nine!

ex: 3,667,554
3+6+6+7+5+5+4=36
3+6=9

3667554/9=407,506

:) actually sarge usually when you add the numbers of a large number together it is a 2 digit number.
I know my multiplication table well enuff for any 2 digit number to say if that 2 digit number is divisible by 9.
This cuts out a step or 2, and does the same thing.

I understand…but maybe someone wants to test the theory starting with a number of about 15 digits!

LC: when you add the numbers of a large number together it is a 2 digit number

S: test the theory starting with a number of about 15 digits

Such as 888,888,888,888,888? That's 120 for Sarge's scenario. Looks like a 3 digit number LC.

Yea Pooga it is a 3 digit number.
when you have any number divisible by 9 an easy way to see if it is divisible by 9 is cross out the 9's then cross out the numbers that add up to 9 such as a 4 and a 5
9 - 8's in your number pooga that brings your number down to 888,888 I see that easy enuff not divisible by 9 when the digits are added up.

another problem with what sarge asked about 15 digits. how many times do you have a 15 digit number.. divided by 9 in the real world. if you have a 15 digit number needing to be divided.. it is by a bigger number than 9.