Hey guys what's up? I'm new to the course and very interested in learning however I can. I'm looking at the second assignment which asks to create a program to find the 1000th prime number and I'm stuck thinking on it. Can someone help me out?

Question

anonymous · Answer

Hello sora , you replied under my question, I'm sorry I can't help , i think we're talking about two different sections

woodrow73 · Answer

To find whether a number is prime or not, we need to see whether it is divisible by a number besides 1 or itself.  A good place to start might be making a function that checks whether a given number is prime or not.  After that function, you could make a loop that keeps track of how many prime numbers have been found, and stop at the 1,000 mark.

There are also many ways to go about the same problem.

sora_89 · Answer

last time I tried it kept going none stop...

sora_89 · Answer

sorry I thought it was the same question... okay i've finally succeeded in the prime number generator but I have to ask is there a way to number them in the list so I wouldn't have to count the "1000th" prime? I see it's 7919 but I had to to actually count to see that!

rsmith6559 · Answer

Python has a function len() which returns the length of whatever is put in the parenthesis:

len( yourList )

There's one little math fact that can REALLY speed your program up:  All non-prime numbers will factor down to prime numbers.

anonymous · Answer

I ran a counter to keep track of where I was in the calculation. Here's my blog post about it. http://exemplaretutoring.com/2016/02/01/finished/ my program lists all the primes up to 7919 in this version (skipping 2) To display the 1000th prime number, i just need to write... if count == 999: print x I wrote comments with // like java which is what I'm used to. forgot python is # for comments

rsmith6559 · Answer

Pretty slow program, huh?  There are simple ways to get it to run much faster:

time ./primes2.py 1000
7919

real	0m0.028s
user	0m0.016s
sys	0m0.008s

anonymous · Answer

yupp. it is pretty damn slow. I've seen some other solutions but they were beyond what I knew at the time. Also there's a solution involving sqrt I see online

woodrow73 · Answer

I'm pretty sure when you test whether a number has any factors or not, you only need to check the numbers (equal maybe) or below the sqrt.

rsmith6559 · Answer

dcaligiuri, if you want to play with it, read the last part of my first post.

anonymous · Answer

seems interesting. I'll look into it soon. Right now I'm working on the Biology String problem - which is of special interest to me since I majored in Biology!