The numbers we use are Arabic numbers. the arabs popularized these numbers which were actually used by phonecian traders to count and keep track of their trading accounts. the phonecian numbers are based on their angles.
1 - one angle
2 - two angles etc.
but these are based on older phonecian numbers. the numbers which we use are of the newer versions of phonecian numbers.
1 5 1
It is formed by the number of angles in each letter
number 1 has I angle
number 2 has 2 angles and so on
while number 0 has no angles
if you have further doubts you can see this picture.............
1 5 1