## 2 May 2018

### One

$1$ is the identity element for multiplication of real numbers.

$1$ is not a prime number! By definition, a prime number has exactly two divisors: $1$ and the number itself.

$0!=1$, even as $1!=1$.

$\log_a a=1$, for all $a \in \mathbb R$.

$a^0=1$, for all $a \in \mathbb R\backslash \{0\}$.

$1$ is the measure of the radius of the unit circle and $\sin^2x+\cos^2x=1$.

Note the results of the following multiplications:

$1 \times 1 =1$.
$11 \times 11=121$.
$111 \times 111=12,321$.
$1,111 \times 1,111=1,234,321$
$\cdots$

They are all palindromic numbers, i.e., numbers that remains the same when its digits are reversed and which is attributed good luck.