In summary, I am having a problem where I read what I expect to be an NSNumber from an NSArray contained in a property list and instead of getting a number such as '1', I get what looks to be a memory address (i.e. '61879840'). The numbers are clearly correct in the property list. Below is my process for creating the property list and reading it back.

Creating the property list

I have created a simple Objective-C property list with arrays of integers within one root array:

<array>
  <array>
    <integer>1</integer>
    <integer>2</integer>
  </array>
  <array>
    <integer>1</integer>
    <integer>2</integer>
    <integer>5</integer>
  </array>
  ... more arrays with integers ...
</array>

The arrays are NSArray objects and the integers are NSNumber objects. The property list has been created and serialized using the following code:

// factorArray is an NSArray that contains NSArrays of NSNumbers as described above
// serialize and compress factorArray as a property list, Factors-bin.plist
NSString *error;
NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                        NSUserDomainMask, YES)
                      objectAtIndex:0];
NSString *plistPath = [rootPath stringByAppendingPathComponent:@"Factors-bin.plist"];
NSData *plistData = [NSPropertyListSerialization
                     dataFromPropertyList:factorArray
                     format:NSPropertyListBinaryFormat_v1_0
                     errorDescription:&error];

Inspecting the created plist, all values and types are correct.

Reading the property list

The property list is read in as Data and then converted to an NSArray:

NSString *path = [[NSBundle mainBundle] pathForResource:@"Factors" ofType:@"plist"];
NSData *plistData = [[NSData alloc] initWithContentsOfFile:path];
NSPropertyListFormat format;
NSString *error = nil;
NSArray *factorData = (NSArray *)[NSPropertyListSerialization
                                  propertyListFromData:plistData
                                  mutabilityOption:NSPropertyListImmutable
                                  format:&format
                                  errorDescription:&error];

Cycling through factorData to see what it contains is where I see the erroneous integers:

for (int i = 0; i < 10; i++) {
  NSArray *factorList = (NSArray *)[factorData objectAtIndex:i];
  NSLog(@"Factors of %d\n", i + 1);
  for (int j = 0; j < [factorList count]; j++) {
    NSLog(@"  %d\n", (NSNumber *)[factorList objectAtIndex:j]);
  }
}

I see all the correct number of values, but the values themselves are incorrect, i.e.:

Factors of 3
  61879840 (should be 1)
  61961200 (should be 3)
Factors of 4
  61879840 (should be 1)
  61943472 (should be 2)
  61943632 (should be 4)
Factors of 5
  61879840 (should be 1)
  61943616 (should be 5)