math

Math is the language developed exactly for that, to be an unambiguous, standard way to represent extremely complex, abstract concepts.

In the example above, both the summation and the for loop are simply

a_1 + a_2 + ... + a_n

Math is the language to explain, programming languages is to implement it in a way that can be done by computers. In a real case scenario is more often

sum(x)

or

x.sum()

as a for loop is less readable (and often unoptimized).

If someone doesn't know math he can do the same as those who don't know programming: learn it.

Learning barrier of math is actually lower than programming