CREATE TABLE TableName (
[tID] [int] IDENTITY (1, 1) NOT NULL ,
[dat] INT,
[ProperID] AS ('I' + CAST([tID] as varchar))
) ON [PRIMARY]
GO

----------- WITH PADDING
CREATE TABLE [dbo].[RCTIPeriods](
	[rctiPeriodID] [int] IDENTITY(1,1) NOT NULL,
	[InvoiceNo] AS ('H' + RIGHT('00000000'+ CAST(rctiPeriodID AS VARCHAR(6)), 6)),
	[rctiMonth] [int] NULL,
	[rctiYear] [int] NULL,
 CONSTRAINT [PK_RCTIPeriods] PRIMARY KEY CLUSTERED 
(
	[rctiPeriodID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]