Summation of Summation: Calculating p^j*p^i

[gmmstr827]

Calculate the summation of i=1 to inf of the summation of j=i to inf of p^(j+i).
Yes, it is the summation of a summation. p^(j+i) can be separated into (p^j)*(p^i).

 

[mathman]

Write k=j-i, then you need to sum p^2i+k with k=0 to ∞ and i=1 to ∞.