An ISBN ( International Stanadard Book Number) is a ten digit code which uniquely identifies a book. The first nine digits represent the Group, Publisher and Title of the book and the last digit is used to check whether ISBN is correct or not.
Each of the first nine digits of the code can take a value between and (inclusive). Sometimes it is necessary to make the last digit equal to ten; this is done by writing the last digit of the code as . To verify an ISBN, calculate times the first digit, plus times the second digit, plus times the third and so on until we add time the last digit. If the final number leaves no remainder when divided by , the code is a valid ISBN.
For example:
Since leaves no remainder when divisible by , hence it is a valid ISBN.
The problem: Let be the prime factorization of the number of valid ISBN codes possible. Find the sum of powers of the prime factors in .
Details and assumptions
If the number of codes would have been , then would have been and hence the answer would have been . However, is not the answer. :(
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Whatever the first 9 digits are there will be exactly 1 choice of the 10th digit which will cause the summation to be divisible by 11 since the final value can take all 11 residues modulo 11. So every selection of the first 9 digits gives rise to exactly 1 valid ISBN, and each digit can be 0 through 9, ie. 10 possibilities, so there are 1 0 9 = 2 9 × 5 9 valid ISBNs, so the answer is 9 + 9 = 1 8