"The best number is 73. Why? 73 is the 21st prime number. Its mirror (37) is the 12th and its mirror (21) is the product of multiplying 7 and 3. ... In binary, 73 is a palindrome, 1001001 which backwards is 1001001" (с) The Big Bang Theory
+ много других значений этого числа http://en.wikipedia.org/wiki/73_(number)