Glucagon is a polypeptide, not a simple molecule with a chemical formula in the traditional sense. Its structure is defined by the sequence of amino acids that make up the protein. The amino acid sequence fully defines its structure.
Therefore, the chemical "formula" for glucagon is best represented by its amino acid sequence:
NH2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr-COOH
This sequence represents the linear arrangement of the 29 amino acids that constitute the glucagon molecule. While it's possible to calculate the empirical formula based on the atomic composition of each amino acid, it would be an extremely large and unwieldy formula that doesn't offer much practical information compared to simply stating the amino acid sequence.
