View Compilation Error

0_0_36854069_11266.cpp: In function 'int s2(int)':
0_0_36854069_11266.cpp:8:59: error: 'ni' was not declared in this scope
 inline int s2(int x){return 1ll*x*(x+1)%mod*(2ll*x+1)%mod*ni%mod;}
                                                           ^