Are the subcarrier indices symmetric?

[kongdd5]

According to IEEE Standard 802.11n-2009, I consider that the subcarrier indices are not symmetric when an OFDM system is sending packets through a bandwidth of 20MHz, but are symmetric when the system is using the 40MHz bandwidth. Am I right here? I would appreciate it if anybody could tell me whether what I think is right or not.

[jadhavhninad]

Hi! Did you figure out about it and if not , could you point to where exactly in the 802.11n-2009 document does it talk about it?