;
; Function to calculate and return the check digit of an NPI.
; The check digit is calculated using the Luhn Formula for
; Modulus 10 "double-add-double" Check Digit. A value of 24 is
; added to the total to account for the implied USA (80840) prefix.
NPI(XUSQI,XUSIEN,XUSDATE)
; Retrieve the NPI value for a qualified identifier entity.
;
; Function to validate the format of an NPI number. It checks the
; length of the number, whether the NPI is numeric, and whether
; the check digit is valid.