Human memory - remembering sequences of letters vs numbers There are 10 digits and 26 letters. In computer science you'd need 4 bits to store a digit value and 5 bits do store a letter value.

Does the same apply to human brain? Is a statistical person able to remember more digits than letters, or is there no difference? Or maybe it varies from person to person?
I am not sure I completely understood your question but I will try to answer it. Different numbers and different letters can be easier or harder to remember based on the order, meaning that, depending on their sequence, it can be either way.
Ex. 
a r d q
is easier to remember than
9 4 6 0
but
z n k r
is harder to remeber than
9 8 3 0.
This is because the letters are used in the English language in a way that allows you to make them into a certain sound but only if you have the right letters.

I hope that was helpful (even though it has been almost two years),