Ricin is a protein (actually, two proteins). You don't generally give chemical formulas for large molecules like that, because they're so large that the structure is more important than the number of atoms. Proteins are specified by amino acid sequences.

Presumably, you could tot up the Cs, Hs, Ns, and Os (plus the occasional S) in the amino acid sequence and come up with a thing. But that's left as an exercise for the reader who can read this.