103 is an integer that follows 102 and precedes 104. As a counting number it is often referenced in basic sequences and lists — see the entry for natural numbers for context. In everyday numbering it appears in addresses, labels, and ordinal uses without special notation.
Mathematical properties
In arithmetic 103 is a prime: it has no positive divisors other than 1 and itself. It is the 27th prime number and sits among primes often studied for their distribution. In modular terms 103 is congruent to 1 modulo 6, and like other primes it plays a role in elementary number theory and computational examples; additional technical classifications are treated in specialized sources such as prime lists and sequences.
Prime quadruplet
103 is part of one of the closest possible clusters of four primes greater than three, called a prime quadruplet. The pattern takes the form p, p+2, p+6, p+8; the quadruplet including 103 is 101, 103, 107, 109. This grouping is of interest in the study of prime gaps and local prime distributions — see more about prime quadruplets.
Occurrences outside pure mathematics
Numbers often gain additional significance through other fields. The chemical element with atomic number 103 is lawrencium (Lr), a synthetic, radioactive element named after Ernest Lawrence; it appears in tables and discussions of the actinides and transactinide elements (element information). In astronomy, Messier 103 designates a compact open cluster in the constellation Perseus and is a common target for amateur observation. In computing, the HTTP status code 103 is defined as "Early Hints" and serves a role in modern web performance techniques.
Because 103 is compact and prime, it is often used in examples, puzzles, and coding exercises where simple, noncomposite integers are required. Its membership in a prime quadruplet makes it a convenient illustrative case when discussing small prime clusters.