qptech blog

Here's the code. I wrote this while just playing around with python and I never intended it for use in any serious project, so don't critisize the code too much.

This is the code that generates and tests palindromes, printing them if they're prime:

def palinprimes(size=5):
 print
 linelen=0
 len2=size/2
 len1=len2+size%2
 fdigs="1379"
 odigs="0123456789"
 omax = len(odigs)
 for fn in range(len(fdigs)):
  fstr = fdigs[fn]
  odone=False
  ocount=[0]*(len1-1)
  while not odone:
   ostr=""
   if len1 > 1:
    for on in ocount:
     ostr = ostr + odigs[on]
    index=len(ocount)-1
    ocount[index] = ocount[index]+1
    while ocount[index] >= omax:
     ocount[index]=0
     index = index -1
     if index < 0:
      odone = True
      break
     ocount[index] = ocount[index]+1 
   else:
    odone = True
   numstr=fstr+ostr
   for index in range(len1-len2,len1):
    numstr = numstr + numstr[len1-index-1]
   if primes.primetest(long(numstr)):
    linelen=linelen+len(numstr)+1
    if linelen>80:
     print
     linelen=len(numstr)+1
    print numstr,     

The one parameter that this function takes (defualts to 5) sets the size (in digits) of palindromes to test. It will test all the palindromes of that size. I don't make any guarantees that my function will generate every palindrome, or that it will correctly find the ones that are prime. But I am quite certain that it does both.

Here is the code to test the prime numbers - it's my entire prime test module including 4 functions (not all of which are required for the palindrome function, but I include them here anyway.)

from math import sqrt
primelist=[2,3,5,7]

def addprime(min=1):
 candidate=primelist[-1]
 if min==1:
  min=primelist[-1]+2
 while min >= primelist[-1]:
  primefound=0
  while primefound==0 :
   isprime=1
   candidate=candidate+2
   index=0
   while isprime == 1 and primelist[index] ** 2 <= candidate :
    if candidate % primelist[index] == 0:
     isprime = 0
    index = index + 1
   if isprime == 1:
    primefound = 1
    primelist.append(candidate)


def listprimes(start,end):
 if primelist[-1] ** 2 < end:
  print "Expanding test list"
  addprime(int(sqrt(end)))
 print
 linelen=0
 num = start
 if num%2 == 0:
  num = num + 1
 while num <= end:
  isprime=1
  index=0
  while isprime == 1 and primelist[index] ** 2 <= num:
   if num % primelist[index] == 0:
    isprime = 0
   index = index+1
  if isprime == 1:
   pstr=str(num)
   linelen = linelen + len(pstr) + 1
   if linelen > 80:
    print
    linelen=len(pstr) + 1
   print pstr,
  num = num + 2

def primetest(num):
 if num < primelist[-1]:
  return primelist.count(num) > 0
 
 if primelist[-1] ** 2 < num:
  addprime(int(sqrt(num)))
 for x in primelist:
  if num % x == 0:
   return False
 return True

def primesofdigits(maxdigits=5):
 addprime(int("9"*maxdigits))
 rlist=[]
 digits=1
 index=0
 count=0
 while digits <= maxdigits and index < len(primelist):
  if len(str(primelist[index])) == digits:
   count = count + 1
  else:
   rlist.append(count)
   count = 1
   digits = digits + 1
  index = index + 1
 return rlist

This is my python code, you should be able to copy it into a file named "primes.py" and import it into the python interpreter (import primes). If you have any problems with the code here and can't make any sense of it, just email me (If you have my email address). Or make your request in a comment and I'll see what I can do for you.

This blog layout is not good for code listing, so make of it what you can.

I had the palindrome function in another module, but you should be able to add it to the primes.py module and call it as primes.palinprimes(5) You may have to change "primes.primetest(long(numstr))" to "primetest(long(numstr))" but it should work as is.