CODEWITHSUNDEEP
python
Jimmy
Jimmy

Reputation: 41

How to generate prime twins using python with basics?

I need to generate prime twins in python but I can only use basics (if, elif, else, for, print. I cannot use while, def, return or break etc.

I wrote this code but it only works under 100, If I want a range up to 1000 it doesn't work and I have no idea how to do it without putting there hundreds ifs'.

Could you please help me?

I tried this:

for i in range (2,100):
    j=i+2
    primetw=True
    if i%2 == 0 or i%3==0 or i%5==0 or i%7==0:
        primetw=False
    if j%2 == 0 or j%3==0 or j%5==0 or j%7==0:
        primetw=False
    if i==3 or i==5 or j==5:
        primetw=True
    if primetw==True:
        print(i,j)

Which has this output:

3 5
5 7
11 13
17 19
29 31
41 43
59 61
71 73

Upvotes: 0

Views: 1693

Answers (2)

Jimmy
Jimmy

Reputation: 41

I figured it out this way.

for i in range (3,101):
    twin = True
    for j in range (2,i):
        if (i % j) == 0 or ((i+2) % j) == 0:
            twin = False 
    if twin == True:
        print (i,i+2)

Output is:

3 5
5 7
11 13
17 19
29 31
41 43
59 61
71 73

Upvotes: 0

jpuriol
jpuriol

Reputation: 382

Here you have an example implementation.

First calculates all prime numbers under N using the sieve of Eratosthenes, and then it finds twin primes. It's probably not the most efficient implementation by I think is good enough for educational purposes.

N = 1000

##
# Find primes using the sieve of Eratosthenes
##
isPrime = [False, False]
for _ in range(2, N):
    isPrime.append(True)
    
for candidate in range(2, N):
    if isPrime[candidate]:
        for i in range(candidate+1, N):
            if i % candidate == 0:
                isPrime[i] = False

primes = []
for i, v in enumerate(isPrime):
    if v:
        primes.append(i)

##
# Calculate twin primes
##

twinPrimes = []
for prime in primes:
    if prime + 2 in primes:
        twinPrimes.append((prime, prime + 2))

print(twinPrimes)

Upvotes: 1

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