Note: RecId stands for Record Identifier. It is often called RowId (row identifier). It is a unique and incremental value stored with each and every row of the table.
Table index properties
The following table describes the properties that are available for indexes on tables.
* AllowDuplicates
If you set this property to Yes, the index can be non-unique. If you don't create at least one unique index, a unique index is created by combining the first index and the RecId.
* CreateRecIdIndex
Specify whether an index on the Record ID field is created.
Incorrect:
Not A:
Account numbers fields have the AccountNum data type.
Reference:
https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/dev-ref/application-explorer-aot-properties
https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/add-index