155 (number) explained

Number:	155
Divisor:	1, 5, 31, 155

155 (one hundred [and] fifty-five) is the natural number following 154 and preceding 156.

In mathematics

155 is:

a composite number
a semiprime.
a deficient number, since 1+5+31=37<155.

10011011₂

has a total of 5 ones in it.

There are 155 primitive permutation groups of degree 81.

If one adds up all the primes from the least through the greatest prime factors of 155, that is, 5 and 31, the result is 155. Only three other "small" semiprimes (10, 39, and 371) share this attribute.

In the military

was a United States Navy Admirable-class minesweeper during World War II
was a United States Navy Wickes-class destroyer during World War II
was a United States Navy General G. O. Squier-class transport during World War II
was a United States Navy Buckley-class destroyer escort during World War II
was a United States Navy during World War II
was a United States Navy four-master wooden schooner during World War II
155mm artillery, a common caliber

In sports

The maximum possible score in a single break in snooker, with a free ball at the start of the break (147 is the highest possible without a free ball)

In transportation

Alfa Romeo 155, a compact executive car produced from 1992 to 1998
Seattle Bus Route 155
London Bus Route 155
The British Rail Class 155 is a diesel multiple unit British train
Blériot 155 was a French airliner of the 1920s
155th Street, Manhattan, New York
155th Street New York City Subway stations:

In other fields

155 is also:

The year AD 155 or 155 BC
155 is the number for the International Operator in the United Kingdom
155 is the number for the emergency medical services in the Czech Republic and Slovakia
155 AH is a year in the Islamic calendar that corresponds to 771 - 772 CE
155 Scylla is a main belt asteroid
Europium-155 is a radioisotope or Europium and fission product with a half-life of 4.76 years
155, a 2007 song by the band +44
The dialing code for Obihiro, Japan
The atomic number of an element temporarily called unquintquinttium
155 North Wacker is a 46-story skyscraper in Chicago
Wolseley No. 155, Saskatchewan, is a rural municipality in Canada