155 (number)
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155 is a natural number that comes after 154 and before 156. It is a composite number, meaning it has factors other than 1 and itself.
In decimal form it consists of three digits: 1, 5, and 5. The sum of its digits is 11. Because it ends in 5, it is always divisible by 5.
Mathematical properties
The prime factorization of 155 is 5 × 31. Both of these are prime numbers, so 155 is a semiprime (a product of exactly two primes). Its divisors are 1, 5, 31, and 155; the sum of its divisors is 192.
155 is an odd number because it cannot be divided by 2. It is not a perfect square, since 12 squared is 144 and 13 squared is 169.
General uses
Like other numbers in everyday range, 155 is used in counting, measurement, notation (such as for anniversaries or road numbers), and identification (such as emergency telephone numbers in some countries). The meaning of such uses depends on the system being applied and is not a mathematical property.