# What was Cayley's formula for the number of invariants? (Lost Formula!?)

I need to find Cayley's formula for the number of linearly independent invariants of homogenous polynomials. This is a combinatorial formula. He is believed to have discovered it in 1854. Unfortunately I can't find it online and it is not available in any book that I know of. Note that this formula is different from the formula used for graphs.