Do you ever wonder why our numbers are so different from our letters? A one (1) is like a lowercase ‘l’, but do you ever confuse the two? A two (2) and a five (5) are something like an ‘s’, but how distinct, with angles and slants where there ought to be curves. Sevens (7) look like inverted uppercase ‘L’s except for that odd direction of the longer stem. I often confuse a six (6) for an uppercase ‘G’, though a ‘G’ is much grander and stately for having that right angle at the tip of the curve. Letters are as alike and similar to numbers as hearing a sound through the air to hearing it through the water. Almost numbers are a foreign rendering of a concept, foreign to the alphabet we own. I venture to guess that numbers are a later invention, and carry less meaning in their shape.
To God be all glory,
Lisa of Longbourn
Lisa of Longbourn 
Well, for a start, our alphabet and our numerals have different origins. The alphabet you’re typing in now is derived from the script used by the Romans, via several medieval developments. The *numbers* one through to whatever have been in use for just as long, but the numerals used to represent them until the fourteenth century were what we now call ‘Roman Numerals’: I, II, III, IV, V etc.
Currently, we represent numbers with Arabic Numerals, adopted by the west in the late medieval era. It’s much, much easier to do complicated arithmetic with Arabic numerals, not least because the Arabs had a numeral- and a concept- to represent Zero.
Arabic Numerals, when used by Arabs who wrote in Arabic script, wouldn’t have suffered from the same confusion with letters which happens when they’re used with the Roman alphabet.