That problem

challenge.py

#If the integers from 1 to 999,999,999 are written as words, sorted alphabetically, and concatenated, what is the 51 billionth letter?
#where strings have no spaces
import time

singles = ["", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"]
singles.sort()

teens = ["ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen",
         "seventeen", "eighteen", "nineteen"]
         
teens.sort()

decades = ["twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"]
decades.sort()

def get_full_decade():
    for x in decades:
        for y in singles:
            yield x + y;
            
    
def create_century():
    c = [x for x in get_full_decade()]
    c.extend(singles)
    c.extend(teens)
    c.sort()
    return c

century = create_century()    
    
def get_hundreds():
    for x in century:
        if not x == "":
            yield x
        if not x in singles:
            continue
        for c in century:
            if not x == "": 
                yield x + "hundred" +  c
                

def get_thousands():
    for x in get_hundreds():
        yield x
        yield x + "thousand"
        for y in get_hundreds():
            yield x + "thousand" + y
            

def get_millions():
    for x in get_hundreds():
        yield x
        yield x + "million"
        for y in get_thousands():
            yield x + "million" + y
            

#base 1
def main(index_to_find):
    count = 0;
    start = time.time()
    for x in get_millions():
        prev = count   
        count += len(x)
        if count >= index_to_find:
            idx = index_to_find - prev
            print "this is the number ", x
            print "this is character", x[idx - 1]
            print "elapsed: ", time.time() - start
            break