145

145 is a natural number that follows 144 and precedes 146. It is an odd composite number with prime factorization 5 × 29, and its divisors are 1, 5, 29, and 145. Because it is the product of two distinct primes, 145 is a semiprime.

In base representations, 145 is written as 145 in decimal, 10010001 in binary, 221 in octal, and 0x91 in hexadecimal. In Roman numerals, it is represented as CXLV. It can be expressed as 12^2 + 1, i.e., one more than a square.

In modular arithmetic, 145 ≡ 1 mod 4 and 145 ≡ 1 mod 16, while 145 ≡ 0 mod 5 and 145 ≡ 0 mod 29. The Euler totient is φ(145) = (5−1)(29−1) = 112. The number of positive divisors is τ(145) = 4, and the sum of divisors is σ(145) = 180.

Historically, 145 can denote a year in the common era (145 CE) or a year in the BC era (145 BCE), occurrences typical in historical chronology. In general usage, 145 appears in various contexts such as model numbers, identifiers, or route designations, though there is no single universally defining significance attached to the number.