While studying sequences and series, I came across summations of geometric series. I am able to derive the sum of a geometric progression and that of arithmetico–geometric sequence.
But what do you call a series where the $i^{th}$ term is $a^{i^2}$? And how can we evaluate its sum?
$$ S = \sum_{i=0}^{n-1}a^{i^2} $$
I tried multiplying $S$ by $a$ and differentiating it by $a$ but to no avail.