p27

p27.py

import os 

primes=set()

def p(n):
	while n%2 == 0:
		n = n//2
	if (n == 1): return True
	limit = n//2
	for j in range(3, limit, 2):
		while n%j == 0:
			n = n//j
	return n != 1

def preComputePrimes():
	global primes
	fname="primesTill100K.txt"
	if os.path.isfile(fname):
		with open('primesTill100K.txt', 'r') as filehandle:
		    primes = set([int(cur.rstrip()) for cur in filehandle.readlines()])
		print("primes loaded form file ", len(primes))
		return
	print("no cache, computing primes")
	primes.add(2)
	for j in range(3, 100000, 2):
		if p(j):
			primes.add(j)
	print("count of primes ", len(primes))
	print("writing to file")
	with open('primesTill100K.txt', 'w') as filehandle:
		filehandle.writelines("%d\n" % p for p in primes)

def eval(a, b, x):
	val = x*x + a*x + b
	if val > max(primes):
		print("VAL exceeding primes max",val,a,b)
	return val

def numOfConsecutivePrimes(a,b):
	primeCount = 0
	for n in range(0,1000):
		if eval(a,b,n) in primes:
			primeCount+=1
	return primeCount
	

def run_p27(u):
	max = 0
	ans = 0
	for a in range(-u+1, u):
		print("running for a ",a)
		for b in range(-u, u+1):
			cur = numOfConsecutivePrimes(a,b)
			if  cur > max:
				max = cur
				ans = a*b
				print(a,b, a*b, max);
	print("p27 answer: ",ans)


preComputePrimes()