View Compilation Error

0_0_20525356_6476.cpp: In function 'int main()':
0_0_20525356_6476.cpp:9:76: error: 'a6' was not declared in this scope
     int b[10][4]={{0},{1},{6,2,4,8},{1,3,9,7},{6,4},{5},{6},{9,3,1,7},{4,2,a6,8},{1,9}};
                                                                            ^