2

2
Basic Information
Cardinal Number	two
Ordinal Number	second
Roman Numeral	II
Greek Numeral	Β´
Factorization	2
Different Representations
Binary Form	102
Ternary Form	23
Quaternary Form	24
Quinary Form	25
Senary Form	26
Septenary Form	27
Octal Form	28
Nonary Form	29
Undecimal Form	211
Duodecimal Form	212
Tridecimal Form	213
Quattuordecimal Form	214
Quindecimal Form	215
Hexadecimal Form	216
Septendecimal Form	217
Octodecimal Form	218
Novemdecimal Form	219
Vigesimal Form	220
Unvigesimal Form	221
Duovigesimal Form	222
Trevigesimal Form	223
Quattuorvigesimal Form	224
Quinvigesimal Form	225
Hexavigesimal Form	226
Septenvigesimal Form	227
Octovigesimal Form	228
Novemvigesimal Form	229
Trigesimal Form	230
Untrigesimal Form	231
Duotrigesimal Form	232
Tretrigesimal Form	233
Quattuortrigesimal Form	234
Quintrigesimal Form	235
Hexatrigesimal Form	236
Previous	None
Current	2
Next	3

2 is the first prime number in the base ten numbering system. It is said to be the only even prime number, as all other even numbers are divisible by 2, making them composite.

Proofs

• — 2 can be divided by 1.

• — 2 can be divided by 2.

• Therefore it only has two factors.

Every even number is divisible by 2. Therefore, the only even prime is 2 because all other even numbers will be divisible by at least three factors - itself, 2, and 1.

Unique Properties

• 2 is the only prime number without an "e" in its name. This is because 2 is the only even prime number, and all odd numbers have an e in their name.
• A number is called even if, and only if, it is divisible by 2.
• $2+2=2\times2=2^2$
• $\sum_{k=1}^\infty\frac{1}{k^2} \not= 2$
• $\sum_{k=0}^\infty\frac{1}{2^k} = 2$

As an Exponent of Mersenne Number

$2^2-1$, which is the number 3, is a prime number. It is the 1st Mersenne Prime.

Relationship with other numbers

The numbers before

• There are no prime numbers before 2. 
• 1, the number before 2, is not a prime number, because it only has 1 factor, itself.

The numbers after

• The next odd number, 3, is a prime number.
• 4 is the first composite number.
• 5, the odd number following 3, is a prime number.

Usage

Science

• 2 is the atomic number of helium, meaning that there are two protons and electrons in a helium atom. There are also two neutrons in helium-4, the most common isotope of helium.
• There are two electrons in the first full electron shell of an atom.
• Group two elements are alkaline earth metals. They have a valency of 2.
• Deuterium, an isotope of hydrogen, has an atomic mass of two.

Technology

• 2 is the resin identification code used in recycling to identify high-density polyethylene.

Sports

• In basketball, any shot not outside the three-point field goal is equal to two points, unless the player who threw the ball is fouled while attempting the shot.
• In Association football, the scoring of two goals by one individual in a single match is referred to as a brace.

Prime Numbers 1-1,000