Hi,

How do i get the sum of such a sequence:

$1 + x^{-1} + x^{-3} + x^{-6} + ...$

where the exponents are actually sum of arithmetic progression. i.e.

$x^{-0} + x^{-(0 + 1)} + x^{-(0 + 1 + 2)} + x^{-(0 + 1 + 2 + 3)} + ...$

which can also be expressed as

$\sum_{i=0}^{\infty} x^{-\frac{i(i + 1)}{2}}$

?

Thanks.