Prime numbers quicky

[YT2095]

is it true that all primes end in either 1,3,7 or 9 after a while?

 

I know the 1`st few dont.

[Dhondy]

C'mon, that should be really easy to answer.

 

Any number ending with 2,4,6,8 or 0 will always be divisible by 2, and hence can't be a prime.

 

Similarly, numbers ending with 5 will always be divisible by 5.

 

That leaves numbers ending with 1,3,7 and 9.

[YT2095]

Good, that`s exactly what I thought too, but had to ask in case there were some Exceptions I couldn`t think of (I`m no maths Genius!).

 

Thnx

[Dhondy]

Try this. More challenging.

 

Of all the numbers ending with 1,3,7 or 9, which has the greatest proportion of primes?

[markusariliu]

7 or 1 or both

[cosine]

I really want to know the answer to Dhnondy's question!

[YT2095]

statistically the number 1 as a digit occurs in more numbers than any of the other 9 digits.

 

I would write a program to find the answer to this question but since I`m writing on an old BBC Micro it may be a little difficult to parse and each line to do so will make it even slower running than it already is.