GSM Frequency

GSM900
There are totally 124 frequency points, the sequence number (ARFCNs are 1 to 124). Each end is left with a protection bandwidth of 200KHz (frequency band guard) and Relation of the frequency and the sequence number (n=ARFCN) is as follows

The base-station receives (Uplink frequency) f₁(n)=890.2+(n-1)×0.2 MHz
The base-station sends (Down link frequency)  f₂(n)＝f₁(n)＋45 MHz

Example: ARFCN =12 compute uplink and downlink frequency? 
frequency uplink = 890.2+(12-1) x 0.2 = 892.4 MHz
frequency downlink = 892.4 + 45 = 937.4 MHz
DCS 1800

There are 374 frequency points totally. The sequence numbers（ARFCN）are from 512～885. Relation of the frequency and the sequence number（n）is as follows:

The base-station receives: f₁(n)＝1710.2 +(n-512) × 0.2 MHz

The base-station sends：f₂(n)＝f₁(n)＋95 MHz
please see below table