where is a -Pochhammer symbol and is the partition function P.
Ramanujan's Identity
See also
Partition Function P, Ramanujan's Sum IdentityExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Ramanujan's Identity." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/RamanujansIdentity.html