The Indiction can be calculated by taking the remainder of the year plus 2 divided by 15 and adding 1 to it. So, possible Indiction values are 1 to 15.
For example: the Indiction for the year 1999 is 7 [(1999 + 2) mod 15 + 1 = 7].
The Indiction is only used for determining the first Julian day. This was January 1 of the year -4712; the most recent year for which the Indiction was 1, the Golden Number was I (1), and the Solar Number was 1 too.