Goldbach's other conjecture : Problem 46
It was proposed by Christian Goldbach that every odd composite number can be written as the sum of a prime and twice a square.
What is the smallest odd composite that cannot be written as the sum of a prime and twice a square?
Problem Source : Euler Project
Python Code
import math
def goldbachConjecture():
found = False
def checkPrime(numb):
prime = True
if numb == 1:
return False
for i in range(int(math.sqrt(numb))):
i = i+2
if numb%i == 0:
prime = False
break
if numb == 2:
return True
else:
return prime
def nextOddCompositeNumber(numb):
numb = numb+1
while checkPrime(numb) == True or numb %2 == 0:
numb = numb+1
return numb;
numb = 9
while found == False:
k = 1
goldtrue = False
while numb-2*k**2 > 0 :
if checkPrime(numb-2*k**2) == True:
goldtrue = True
break
k = k+1
if goldtrue == True:
found = False
numb = nextOddCompositeNumber(numb)
else:
found = True
print "smallest odd composite that cannot be written as the sum of a prime and twice a square",numb
goldbachConjecture()
9 = 7 + 2×12
15 = 7 + 2×22
21 = 3 + 2×32
25 = 7 + 2×32
27 = 19 + 2×22
33 = 31 + 2×12
It turns out that the conjecture was false.15 = 7 + 2×22
21 = 3 + 2×32
25 = 7 + 2×32
27 = 19 + 2×22
33 = 31 + 2×12
What is the smallest odd composite that cannot be written as the sum of a prime and twice a square?
Problem Source : Euler Project
Python Code
import math
def goldbachConjecture():
found = False
def checkPrime(numb):
prime = True
if numb == 1:
return False
for i in range(int(math.sqrt(numb))):
i = i+2
if numb%i == 0:
prime = False
break
if numb == 2:
return True
else:
return prime
def nextOddCompositeNumber(numb):
numb = numb+1
while checkPrime(numb) == True or numb %2 == 0:
numb = numb+1
return numb;
numb = 9
while found == False:
k = 1
goldtrue = False
while numb-2*k**2 > 0 :
if checkPrime(numb-2*k**2) == True:
goldtrue = True
break
k = k+1
if goldtrue == True:
found = False
numb = nextOddCompositeNumber(numb)
else:
found = True
print "smallest odd composite that cannot be written as the sum of a prime and twice a square",numb
goldbachConjecture()
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