A 73c file extension is related to the Texas Instruments TI-73 complex number data format. Probably obsolete format.
73C file extension - Texas Instruments TI-73 complex number data
What is 73c file? How to open 73c files?
File type specification:
The 73c file extension is associated with programmable calculators developed by the Texas Instruments.
The 73c file stores complex number for Texas Instruments TI-73 graphics calculator based on popular Zilog Z80 platform.
This 73c file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.