To display indirect block numbers?

Hi all , If I want to display block numbers of a file. For instance file size is 64KB and block size is 4KB. So the data will accommodate in 16 blocks. Now I accessed an array named "i_block[ ]" present in ext2_inode structure. This array stores the block numbers of a file. The first 12 blocks are direct blocks which will store 48KB data of file and the 13th block will be single indirect block which will store the rest of the data. In this way I can directly get the data of 48KB by referring first 12 direct blocks. My question is how can I access this 13th block to get the remaining block numbers which will directly point to rest of the data. -- Regards, Kashish