103 explained.

103 in everyday use

One hundred three is the atomic number of lawrencium, the synthetic element that closes the actinide series of the periodic table. It was first produced at the University of California, Berkeley, in 1961 and named after Ernest Lawrence, inventor of the cyclotron. Only a few atoms at a time have ever been made, so its chemistry is known mostly from painstaking experiments on short-lived samples. Beyond the laboratory, 103 is a common FM radio frequency band position and a routine bus and route number, with no other strong cultural association.

As a number, 103 is prime and forms a twin-prime pair with 101, the two being separated only by the even number 102. It is the smallest three-digit prime whose digit reversal is composite: 301 factors as 7 × 43, whereas 101 reversed is still 101. Adding its digits gives 4, and squaring and adding the digits repeatedly leads to 1, so 103 is also what mathematicians call a happy number.