The most valuable number in a three-number bookend is the first, because it is normally used as an identifier. As a result, the sum of the first two numbers is usually a prime number, which makes it the most valuable.
Examples
The value for the first bookend is 59, because it is a prime number. The value for the second bookend is 70, because it is the sum of two primes (3+7=10). The value for the third bookend is 97, because it is the sum of two prime numbers (5+2=7). The value for the fourth bookend is 345, because it is the sum of two prime numbers (3+5=8).
Once the bookends have been established, the value of a number is determined by examining the last digits of its first two bookends.
The last two digits of the first bookend, + the last two digits of the second bookend, + the last digit of the third bookend = the value of the number. (See above.)
Therefore, 345 + 5 = 350, which is the value of the number with the last two digits "000" and the last digit "5".
Some specific examples
The value of 5055 is the sum of the last two digits of the first and second bookends (5+0+5 = 10).
The value of 2542 is the sum of the last two digits of the first and second bookends (2+5+4 = 11).
The value of 7799 is the sum of the last two digits of the first and second bookends (7+7+9 = 21).
The value of 5439 is the sum of the last two digits of the first and second bookends (5+4+4 = 13).
The value of 4508 is the sum of the last two digits of the first and second bookends (4+0+5 = 9).
The value of 9443 is the sum of the last two digits of the first and second bookends (9+4+3 = 18).
The value of 8999 is the sum of the last two digits of the first and second bookends (9+8+9 = 26).
History
The oldest known instances of the use of three-number bookends in this way are, respectively be359ba680
Related links: