1. The number 73 is the 21st prime number. Its mirror number, 37, is the 12th prime number. Twenty one also includes factors 7 and 3.
2. Also, 37+12=49 (seven squared) and 73+21=94, which is 47×2, 47+2 also being equal to seven squared.
3. The binary of 73 is 1001001 and that of 21 is 10101, both of which are palindromes (word, phrase or number that reads the same backward and forwards).
4. The binary of 73 has 7 numbers and 3 ones.
5. Seventy three is a permutable prime with 37.
6. The atomic number of the chemical element Tantalum is 73.
7. A Saros is a period of 223 synodic months or approximately 18 years, 11 days, 8 hours that is used to predict eclipses of the sun and the moon. The duration of the Saros series 73 contained 73 solar eclipses.
8. It took 73 seconds for the Space Shuttle Challenger OV-099 to explode after launch.
9. If you count the Book of Lamentations as separate from the Book of Jeremiah in the Catholic version, then the Holy Bible has 73 books.
10. The Discordian or Erisian calendar used by the followers of Discordianism has 73 months.
11. The rhythmic clapping at sporting events that precedes ‘Let’s Go!’ is the Morse code for 73 which translates to ‘Best Regards’.
12. We got to know of Dr. Cooper’s admiration for the number in the 73rd episode of The Big Bang Theory.