Question

Ok, so here is my attempt at problem set 1. Can anyone tell me where I went wrong?

import math
number=1
primes = [2]
moduli=[1]
test=3
while number <= 1000:
for prime in primes:
if (test/prime)>=2:
m=test%prime
moduli.append(m)
moduli.sort()
for item in moduli:
if 0==item:
moduli=[]
test=test+2
else:
primes.append(test)
test=test+2
number=number+1
print primes[1000]

Answer 1

ok, so from my understanding you're divising test variables by all primes found so far, right?
when I ran your code it gave me 2039 as the 1000th prime which is too low

Answer 2

it seems that by div/mod by primes results in the code finding primes which actually arent

Answer 3

yeah - if we are testing number x, then it is prime if it is NOT evenly divisible by any prime lower than x/2

Answer 4

yeah

Answer 5

got it working

import math
n=1
primes = [2]
check=0
test=3
while n <= 1000:
for prime in primes:
if test%prime==0:
check=1
if check==1:
test=test+2
check=0
else:
primes.append(test)
test=test+2
check=0
n=n+1

print primes[999]

Answer 6

just ran your code again to print out the primes when it finds them and it gives e.g. 15, 21,27..all divisible by 3, which is in the list as well - seems like that's responsible

Answer 7

yeah, i got rid of the mod check list, and just had it be a binary result - if one of the primes divides evenly into the test number, it changes the check number to 1, which means test number is not prime

Answer 8

cool! I like your solution - mine was much more complicated - gonna take a closer look at it :)

Answer 9

thanks :) . mind posting your sol'n?

Answer 10

sure:

primecount = 0
candidate = 1
while primecount < 999:
candidate = candidate +2
divisor = 3
not_prime = False
while (divisor < candidate/2) and (not_prime == False):
if candidate%divisor == 0:
not_prime = True
## print candidate
## print (' is not a prime')
divisor = divisor+2

if not_prime == False:
## print (candidate)
## print ('is prime')
primecount = primecount +1
print candidate

Answer 11

didn't know about division by primes so divided by all candidates/2 up to the current every time

Answer 12

looks very similar to mine, except for the primes thing. nice.

Answer 13

thx