Mildly Interesting

the article mentions 69 being skipped as well. I assume it's pretty simple, just check it against the list and increment until it's valid.

int getNextOrderNumber(int currentNumber) {
    currentNumber++; 
    while(isBanned(currentNumber)) {
        currentNumber++; 
    } 
    return currentNumber; 
} 

where bool isBanned(int orderNumber) simply checks the order number against the banned list and returns true if it's not allowed.