The total number of possible combinations for an N-digit number on a mobile keypad is calculated by considering the number of choices for each digit. Most digits (2-9) have 3 possible letters, while 0 and 1 have 1 or 0 options respectively. For a general N-digit number, assuming each digit has an average of X options, the total combinations would be X^N. However, if we consider the specific mapping of a standard phone keypad (2-9 having 3 letters each, 0 and 1 having 1 option), the calculation becomes more complex and depends on the exact definition of 'possible combinations' (e.g., if only valid words are considered, or any sequence of letters). If the question implies any sequence of N digits where each digit has a fixed number of options (e.g., 3 for digits 2-9, 1 for 0 and 1), the calculation would be (number of options for digit 1) * (number of options for digit 2) * ... * (number of options for digit N). For a 10-digit number, this would be 10^10 if each digit could be any of the 10 numbers. If we consider the letters on the keypad, and assume each position can be any of the 3 letters for digits 2-9, and 1 for 0 and 1, the calculation would be different. For example, for a 7-digit number, it's often calculated as 3^7, assuming each digit maps to 3 letters. The number 362880 is 10!, which is the number of permutations of 10 distinct items, not directly related to N-digit number combinations on a keypad unless there's a very specific, unstated constraint.