Do this
1 + 1/2 + 1/4 + 1/27 + 1/256 + 1/3125 + 1/46656 + ...
step by step, so I would understand exactly what you mean when you talk about limits and infinite series.
I'm going to assume you mean 1 + 1/4 + 1/27 + ... + 1/n^n + ..., because otherwise it is simply this series with 1/2 added. Now, if the sequence of partial sums of the sequence {1, 1/4, 1/27, ..., 1/n^n, ...} has a limit L, then
1 + 1/4 + 1/27 + 1/256 + 1/3125 + 1/46656 + ... = L
by definition of the sum of a convergent series. For completeness, the sequence of partial sums is {1, 5/4, 139/108, ...}. It appears to have a limit, so L does exist and the series has a sum, by definition.
For any series denoted by the sequence {a1, a2, a3, ...} in general, its sum is the limit of the sequence of partial sums {s1, s2, s3, ...} provided that limit exists, where s1 = a1, s2 = a1 + a2, s3 = a1 + a2 + a3, ...
If the sequence of partial sums does not have a limit, as in the case of 1 + 1/2 + 1/3 + 1/4 + ..., then the expression does not denote a number. But, if it does have a limit, as in the case of 1/2 + 1/4 + 1/8 + ..., then the expression does denote a number, the limit of the sequence of partial sums.
That is the definition of infinite sum I have always used, and it is the definition in every textbook I have seen containing a section on infinite series.