CA Dynamic Signalling

Hi Experts,
Anyone having idea for LTE CA how this number (below image) is decided by eNodeB and the significance?


This is pucch format 1b with channel selection for HARQ feedback in case of 2CC

The UE selects the n1pucch resources to be used from the list based on whether ACK/NACK/DTX need to be sent back for each of the codewords for each CC