Random Array of numbers passed and get consecutive number range

RandomArray.h

NSMutableArray *randomNumbersArray;
randomNumbersArray = [NSMutableArray arrayWithObjects:@(1),@(2),@(4),@(6),@(9),@(11),@(12),@(14),@(15),@(21),@(22),@(23),@(24),@(25),@(27),@(28),@(30),@(31),@(33),@(35),@(36), @(41), @(40), nil];

- (NSArray *)getConsecutiveArray:(NSArray *)originalArray {

    NSInteger startNumber, endNumber;
    NSMutableArray *finalArray = [NSMutableArray array];
    
    for (int index = 0; index < originalArray.count; index++) {
        
        startNumber = [originalArray[index] integerValue];
        endNumber = startNumber;
        
        if (index != originalArray.count - 1) {
            while ([originalArray[index] integerValue] - [originalArray[index + 1] integerValue] == -1) {
                endNumber = [originalArray[index + 1] integerValue];
                index++;
            }
            if (startNumber == endNumber) {
                [finalArray addObject:[NSString stringWithFormat:@"%ld", startNumber]];
            }
            else {
                [finalArray addObject:[NSString stringWithFormat:@"%ld-%ld", startNumber, endNumber]];
            }
        }
    }
    return finalArray;
}