The invention claimed is:1. A communication apparatus comprising:a receiver which, in operation, receives resource allocation information that indicates at least two clusters of resource blocks allocated by a base station apparatus, each cluster including one or more consecutive resource block groups (RBGs), wherein the at least two clusters are located on frequency positions separated from each other, and wherein the resource allocation information includes a combinatorial index that is calculated by using: a starting RBG index (s1) of a first cluster; an index (e1) obtained by adding one to an ending RBG index of the first cluster; a starting RBG index (s2) of a second cluster; an index (e2) obtained by adding one to an ending RBG index of the second cluster; and a number N that is obtained by adding one to a total number of RBGs included in an uplink system bandwidth; anda transmitter which, in operation, transmits data using the at least two clusters based on the resource allocation information.2. The communication apparatus according to claim 1 wherein, when the starting RBG index equals its corresponding ending RBG index, a single RBG is allocated for a cluster with the starting RBG index.3. The terminal apparatus according to claim 1, wherein the combinatorial index is generated based on the following formula:in which M represents the number of clusters allocated in the uplink and is 2, and N represents the number obtained by adding one to the total number of RBGs included in the uplink system bandwidth.4. The communication apparatus according to claim 1, whereina first number of signaling bits are required for the resource allocation information when one is added to the total number of RBGs included in the uplink system bandwidth,a second number of signaling bits are required for the resource allocation information when one is not added to the total number of RBGs included in the uplink system bandwidth, andone is added to the total number of RBGs included in the uplink system bandwidth to obtain the number N used in calculatioin of the combinational index only when the first number is equal to or less than the second number.5. The communication apparatus according to claim 4, wherein when the first number is equal to or greater than the second number, the combinatorial index is calculated by using the total number of RBGs included in the uplink system bandwidth without adding one to it.6. A communication method comprising:receiving resource allocation information indicating at least two clusters of resource blocks allocated by a base station apparatus, each cluster including one or more consecutive resource block groups (RBGs), wherein the at least two clusters are located on frequency positions separated from each other, and wherein the resource allocation information includes a combinatorial index that is calculated by using: a starting RBG index (s1) of a first cluster; an index (e1) obtained by adding one to an ending RBG index of the first cluster; a starting RBG index (s2) of a second cluster; an index (e2) obtained by adding one to an ending RBG index of the second cluster; and a number N that is obtained by adding one to a total number of RBGs included in an uplink system bandwidth; andtransmitting data using at least two clusters based on the resource allocation information.7. The communication method according to claim 6 wherein, when the starting RBG index equals its corresponding ending RBG index, a single RBG is allocated for a cluster with the starting RBG index.8. The communication method according to claim 6, wherein the combinatorial index is generated based on the following formula:in which M represents the number of clusters allocated in the uplink and is 2, and N represents the number obtained by adding one to the total number of RBGs included in the uplink system bandwidth.9. The communication method according to claim 6, whereina first number of signaling bits are required for the resource allocation information when one is added to the total number of RBGs included in the uplink system bandwidth,a second number of signaling bits are required for the resource allocation information when one is not added to the total number of RBGs included in the uplink system bandwidth, andone is added to the total number of RBGs included in the uplink system bandwidth to obtain the number N used in calculatioin of the combinational index only when the first number is equal to or less than the second number.10. The communication method according to claim 8, wherein when the first number is equal to or greater than the second number, the combinatorial index is calculated by using the total number of RBGs included in the uplink system bandwidth without adding one to it.